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Ganita ManjariCh 9 Propositions aur unke Converses

Propositions and their Converses (Propositions aur unke Converses): Class 9 Maths Chapter 9 Hinglish mein

Ganita Manjari Part 2 · Hinglish notes, simulations aur practice · Official NCERT chapter PDF ↗

Published · Updated

  • 45 min
  • 22 practice questions
  • 17 MCQs

Is chapter mein aap kya seekhenge

  • Proposition ko ek aise sentence ki tarah pehchaano jo ya to true ho ya false, aur use 'if X then Y' form mein likho
  • Kisi proposition ke 'if' aur 'then' parts ko swap karke uska converse banao, setting ko bina badle
  • Tay karo ki proposition aur uska converse true hain ya nahi: true wale ko prove karo aur har false wale ke liye counterexample do
  • Samjhao ki ek counterexample kisi claim ko galat kyun saabit kar deta hai, jabki bahut saare matching examples use prove nahi karte
  • Isosceles-triangle theorem aur Baudhāyana–Pythagoras theorem ke converses prove karo
  • Doosri phrasings mein bhi wahi matlab pehchaano, jaise 'X implies Y' aur 'Y when X'

NCERT Mathematics Class 9, Chapter 9, pp. 1–7 par based original companion text. Yeh NCERT se juda nahi hai aur NCERT ne ise endorse nahi kiya hai.

9.1 Propositions aur 'if … then …' form

Kuch sentences check kiye ja sakte hain aur kuch nahi. 'Kolkata Hooghly ke kinaare hai' true hai. '17 ek even number hai' false hai. Lekin 'Please namak pass karo' ek request hai, 'Kya bus late hai?' ek question hai aur 'Biryani sabse achha khaana hai' ek opinion hai. In teeno mein se kisi ko bhi seedhe true ya false nahi keh sakte.

Definition
Proposition

Aisa sentence jo ya to true ho ya false, lekin dono nahi.

Example'91 ek prime number hai' ek proposition hai. Yeh false nikalta hai, kyunki 91=7×13.

To false sentence bhi proposition (कथन) hi ginaa jaata hai. Zaroori yeh hai ki uska ek pakka answer ho, true ya false. Maths ke bahut saare propositions do chhote statements ko if aur then words se jodte hain. Yeh raha ek, jo tumne pichhli class mein prove kiya tha.

TheoremEqual sides ke saamne wale angles

Kisi triangle mein, agar do sides ki length same ho, to un do sides ke saamne wale angles bhi equal hote hain.

If ke baad wale part ko X kaho, aur then ke baad wale part ko Y. Yahan X hai 'do sides equal hain' aur Y hai 'unke saamne wale angles equal hain'. Ab dono parts ko swap karo. Tumhe ek naya proposition milta hai: kisi triangle mein, agar do angles equal hon, to un angles ke saamne wali sides ki length same hoti hai.

Definition
Converse

'If X then Y' ka converse proposition 'if Y then X' hai. Ise 'if' part aur 'then' part ko swap karke banate hain.

Example'Agar koi number 5 par khatam hota hai, to woh odd hai' ka converse hai 'agar koi number odd hai, to woh 5 par khatam hota hai'.

3/3Banana fruit hai lekin mango nahi, isliye converse false hai.

Fig. 9.1'If' card aur 'then' card ko swap karne se proposition apne converse mein badal jaata hai.

Do slots par 'If' aur 'then' likha hai. Pehle step mein orange card X, 'yeh mango hai', If slot mein hai aur green card Y, 'yeh fruit hai', then slot mein; ek panel kehta hai True: har mango ek fruit hai. Doosre step mein dono cards jagah badalte hain, to sentence banta hai 'Agar yeh fruit hai, to yeh mango hai', aur panel poochhta hai ki kya har fruit mango hai. Teesre step mein panel par ek cross, False word aur ek banana dikhta hai: banana fruit hai lekin mango nahi.

Hum aksar 'if X then Y' ko 'X implies Y' likhte hain, ya arrow se: X⇒Y. Arrow ko 'implies' padho. Tab converse (विलोम) hai Y⇒X. Arrow bas doosri taraf point karta hai.

Fig. 9.1 mein ek true proposition ne false converse diya. To is chapter ka bada sawaal hai: kya swap ke baad bhi truth bachta hai? Kabhi bachta hai aur kabhi nahi, jaisa agle sections dikhate hain.

Quick check
3 mein se 1
Inmein se kaun se propositions hain? Jitne sahi hon, sab chuno.
Saare sahi options chuno
Answer dekho
Answer
  • (A) 17 ek prime number hai.
  • (C) Har square ki chaar equal sides hoti hain.
  • (E) 5+3=9
A aur C true propositions hain aur E ek false proposition hai: false sentence bhi proposition hi hai. B ek request hai aur D ek question, isliye dono mein se koi true ya false nahi ho sakta.

9.2 Kya true proposition ka converse bhi true hota hai?

Section 9.1 ke triangle propositions ke pair se shuru karo. Pehla ek theorem hai jo tum pehle se jaante ho. Aage padhne se pehle doosre ko khud settle karne ki koshish karo.

3/4△PQS aur △PRS mein angle, angle aur side match karte hain.

Fig. 9.2Altitude girane se triangle do congruent halves mein bant jaata hai.

Triangle PQR ka apex P upar hai aur Q aur R par equal angles mark kiye gaye hain; note poochhta hai ki kya PQ, PR ke equal hai. Doosre step mein P se QR par ek dashed altitude PS girti hai, aur S par right-angle marks hain. Teesre step mein dono halves, PQS aur PRS, alag-alag colours mein shaded hain aur notes matching parts batate hain: S par dono angles 90 degrees hain, PS common hai, isliye triangles congruent hain. Aakhri step mein PQ aur PR par tick marks aate hain aur note conclude karta hai PQ = PR.

TheoremEqual angles ke saamne wali sides

Agar kisi triangle ke do angles equal hon, to un angles ke saamne wali sides equal hoti hain.

To yahan proposition aur uska converse dono true hain. Kya aisa hamesha hota hai? Ek rozmarra ka proposition try karo.

Example 1NCERT Example 1 · p. 1

Ek city aur uska state

Proposition P: agar koi person Pune mein rehta hai, to woh person Maharashtra mein rehta hai. Iska converse Q likho. Kya P true hai? Kya Q true hai?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

3/3Nagpur ka resident Y mein hai lekin X mein nahi: Q ka ek counterexample.

Fig. 9.3'If X then Y' kehta hai ki X region, Y region ke andar baitha hai. Y mein X ke bahar ka koi point converse ko tod deta hai.

Ek bada blue oval Maharashtra mein rehne wale sab logon (Y) ko dikhata hai aur uske andar ek chhota orange circle Pune mein rehne wale sab logon (X) ko. Pehle step mein sirf do regions dikhte hain, X circle poori tarah Y oval ke andar hai. Doosre step mein Meera ke liye ek dot circle ke andar tick ke saath aata hai, jo Pune mein rehti hai: X mein hona use Y mein rakhta hai. Teesre step mein Nagpur ke ek resident ke liye ek diamond oval ke andar lekin circle ke bahar aata hai, ek cross aur is note ke saath ki yeh Y mein hai lekin X mein nahi: converse ka counterexample.

Nagpur ka resident Q ka ek counterexample hai. Fig. 9.3 jaisi picture mein, 'if Y then X' ka counterexample woh point hai jo Y region ke andar ho lekin X region ke bahar.

Definition
Counterexample

Ek particular case jo proposition ke 'if' part ko true aur 'then' part ko false bana de. Ek akela counterexample saabit kar deta hai ki proposition false hai.

Example'Agar koi number odd hai, to woh prime hai' ka counterexample 9 hai: 9 odd hai, lekin 9=3×3.

Prove karna aur disprove karna bilkul alag-alag level ke kaam hain. Kisi baat ko true kehne ke liye aisa argument chahiye jo har case mein chale, un cases mein bhi jo kisi ne check nahi kiye. False kehne ke liye bas ek case (प्रत्युदाहरण) kaafi hai, chahe kitne bhi doosre cases match karte rahe hon. Isiliye mathematicians counterexamples dhoondhte rehte hain.

Example 2NCERT Example 2 · p. 2

12 aur 4 ke multiples

Yeh raha ek claim P: agar koi whole number 12 se divisible hai, to 4 bhi use divide karta hai. Samjhao ki P sahi kyun hai. Phir uska converse Q likho aur tay karo ki Q sahi hai ya nahi.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check
3 mein se 1
Kaun sa number claim agar 5 kisi number ko divide karta hai, to 15 bhi use divide karta hai ko todta hai?
Answer dekho

Answer (D) 20

20 5 se divisible hai, to 'if' part sahi hai, lekin 15 use divide nahi karta. 30 aur 45 claim se match karte hain, aur 7 to 5 se divisible hi nahi hai, isliye woh claim ko tod nahi sakta.

9.3 Jab dono directions true hon

Kabhi-kabhi converse har test paar kar leta hai. Ek classic case factors ginne se aata hai. Kuch numbers ke factors list karo aur gino: kin numbers ka count odd aata hai?

Example 3NCERT Example 3 · p. 2

Perfect squares aur odd factor counts

Koi bhi positive integer n lo. Claim P: agar kisi whole number m ke liye n=m×m ho, to n ke factors ka count odd hota hai. Iska converse Q: agar n ke factors ka count odd ho, to kisi whole number m ke liye n=m×m hota hai. Dono claims ko 40 aur 36 par test karo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

3/36 khud se pair banata hai, kyunki 6×6=36: count odd hai.

Fig. 9.4Factors pairs mein aate hain. Sirf square ka hi aisa factor hota hai jo khud se pair banata hai.

Numbers ki do rows. Upar wali row mein 40 ke factors hain: 1, 2, 4, 5, 8, 10, 20, 40. Pehle step mein blue arcs 1 ko 40 se, 2 ko 20 se, 4 ko 10 se aur 5 ko 8 se jodte hain: chaar pairs, aath factors. Neeche wali row mein 36 ke factors hain: 1, 2, 3, 4, 6, 9, 12, 18, 36. Doosre step mein green arcs 1 ko 36 se, 2 ko 18 se, 3 ko 12 se aur 4 ko 9 se jodte hain, aur beech mein 6 bina arc ke reh jaata hai. Teesre step mein 6 ke charon taraf ek dashed loop banta hai aur ek note kehta hai 6 × 6 = 36, isliye 36 ke 9 factors hain.

Argument kis direction ko prove karta hai?

n ko kisi bhi factor f se divide karne par ek aur factor n÷f milta hai, aur dono ka product n hota hai. Fig. 9.4 mein har arc aise hi ek factor pair ko jodta hai. Do alag numbers ke beech ka arc do factors cover karta hai, isliye sirf arcs hamesha even number of factors hi ginte hain.

Ab maan lo factors ka count odd hai. Arcs sab kuch cover nahi kar sakte, isliye kisi factor f ka koi arc nahi hai: woh khud apna partner hai, yaani f×f=n. Tab n ek perfect square hai. Yeh argument odd count se shuru hota hai aur square par khatam hota hai, isliye yeh Q ko prove karta hai. P ke baare mein yeh abhi kuch nahi batata.

P prove karne ke liye doosre end se shuru karo. Agar n=f×f, to f khud se pair banata hai. Kya koi doosra number g bhi khud se pair bana sakta hai? Tab g×g=f×f. Lekin agar g>f to g×g>f×f, aur agar g<f to g×g<f×f. Isliye g=f: kisi number ka zyada se zyada ek hi self-paired factor hota hai.

Baaki sab factors do alag numbers ke pairs mein hote hain, jo even count dete hain. Usme ek self-paired factor jodne se total odd ho jaata hai. To P bhi true hai.

Quick check
3 mein se 1
100 ke kitne factors hain?
factors
Answer dekho

Answer 9 factors

1×100, 2×50, 4×25, 5×20 aur 10×10: chaar pairs aur self-paired 10 milkar 9 factors banate hain, ek odd count, jaisa P square 100 ke liye predict karta hai.

9.4 Chaar possible outcomes

Ab tak humne ek true proposition dekha jiska converse false tha, aur aise pairs jahan dono directions sahi hain. Kya aisa ho sakta hai ki proposition false ho aur uska converse true?

Example 4NCERT Example 4 · p. 3

Equal perimeters aur congruent triangles

P: agar do triangles ke perimeters equal hon, to woh congruent hote hain. Q: agar ek triangle doosre se congruent ho, to dono ke perimeters match karte hain. Tay karo ki har ek true hai ya nahi. True wale ko justify karo aur false wale ke liye counterexample do.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

3/3B, A par fit nahi hota, isliye P false hai.

Fig. 9.5Equal perimeters se congruence zaroori nahi hota.

Pehle step mein ek blue right-angled triangle A dikhta hai jiski sides 6, 8 aur 10 cm hain, uske perimeter 6 + 8 + 10 = 24 cm ke saath. Doosre step mein uske paas ek orange equilateral triangle B aata hai jiski sides 8 cm hain, uska perimeter bhi 24 cm hai. Teesre step mein triangle B ki ek dashed copy triangle A ke upar slide hoti hai: outlines match nahi karti, aur note kehta hai 'Same perimeter, not congruent' (perimeter same, lekin congruent nahi).

Examples ko saath-saath rakho, to har combination dikh jaata hai (Table 9.2).

Table 9.2Proposition aur uska converse: chaaron combinations hote hain
Example
Dono trueperfect square ⇒ factors ka count odd (Example 3)
Sirf proposition true12 ka multiple ⇒ 4 ka multiple (Example 2)
Sirf converse trueequal perimeters ⇒ congruent triangles (Example 4)
Dono falseprime ⇒ odd (2 ek even prime hai; 9 odd hai lekin prime nahi)

Seekh yeh hai: proposition true hai ya nahi, yeh jaanne se uske converse ke baare mein kuch pata nahi chalta. Har ek ko alag se check karna padta hai, proof se ya counterexample se. Neeche wala checker tumhe kuch number propositions aur unke converses ko 1 se 100 tak ke numbers par test karne deta hai.

InteractiveConverse checker

Ek menu chhah number propositions deta hai, jaise 'multiple of 12 implies multiple of 4' aur 'prime implies odd'. Do buttons proposition aur uske converse mein se chunne dete hain, aur sentence poora likha dikhta hai. 'Check 1 to 100' dabane par 1 se 100 tak ke numbers ka 10 by 10 grid mark hota hai: jo numbers 'if' part ko true banate hain unki dark outline hoti hai, jo 'then' part ko true banate hain woh shaded hote hain, aur jo number 'if' part ko true aur 'then' part ko false banata hai use counterexample ke roop mein moti orange border aur chhota cross milta hai. Ek status line pehle counterexamples list karti hai, ya batati hai ki 100 tak koi nahi mila aur yeh evidence hai, proof nahi.

Fig. 9.6Ek proposition chuno, use ya uska converse select karo, phir 1 se 100 tak har number ko counterexamples ke liye check karo.
Quick check
2 mein se 1
Har proposition ko us baat se match karo jo uske aur uske converse ke baare mein true hai.

Left mein koi item tap karo, phir right mein uska match.

Answer dekho
Answer
  • 8 ka multiple ⇒ even : sirf proposition
  • teen equal sides ⇒ teen equal angles : dono
  • even ⇒ 4 ka multiple : sirf converse
  • prime ⇒ odd : koi nahi
8k=2×4k even hai, lekin 6 even hai aur 8 ka multiple nahi. Triangle ki teen equal sides theek tabhi hoti hain jab uske teen equal angles hon. 6 even hai lekin 4 ka multiple nahi, jabki 4 ka har multiple even hai. 2 ek even prime hai, aur 9 odd hai lekin prime nahi.

9.5 Baudhāyana–Pythagoras theorem aur uska converse

Tumne Baudhāyana–Pythagoras theorem kai baar use kiya hai, jaise Part 1 ke Chapter 1 mein points ke beech distances nikaalne ke liye. Yeh raha use dhyaan se state karne ka ek tareeka.

TheoremBaudhāyana–Pythagoras theorem

Sides a, b aur c wale triangle mein: agar sides a aur b ke beech ka angle right angle ho, to a2+b2=c2.

Example 5NCERT Example 5 · p. 4

Theorem ka converse likhna

Upar state kiye gaye Baudhāyana–Pythagoras theorem ka converse likho.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Converse sahi likhna sirf aadha kaam hai: use abhi prove bhi karna hai. Neeche wala proof khud theorem ko use karta hai, ek doosre triangle par jo hum banate hain.

4/4Teeno sides same, isliye ∠R=∠F=90∘.

Fig. 9.7Legs a aur b wala ek right triangle banao; uska hypotenuse c hi nikalta hai.

Left mein triangle PQR apni sabse lambi side PQ = c par tika hai, QR = a, PR = b, aur upar ke vertex R par question mark hai; upar ka label kehta hai a squared plus b squared barabar c squared. Doosre step mein right mein ek right triangle DEF aata hai, jiska right angle F par hai, EF = a aur DF = b. Teesre step mein uski teesri side DE par c likha jaata hai, kyunki DE squared barabar a squared plus b squared hai, jo c squared ke barabar hai. Aakhri step mein R par question mark ki jagah right-angle mark aa jaata hai: triangles SSS se congruent hain, isliye angle R barabar angle F, yaani 90 degrees.

TheoremBaudhāyana–Pythagoras theorem ka converse

Agar kisi triangle ki sides is relation ko satisfy karti hain: a2+b2=c2, to side c ke saamne wala angle right angle hota hai.

Dhyaan do ki proof original theorem ko sirf is triangle par use karta hai: △DEF, jo right-angled hai kyunki humne use aise hi banaya. Yeh ∠R ke baare mein kuch bhi assume nahi karta, isliye argument gol-gol nahi ghoom raha.

Example

Kya koi right angle hai?

In triangles mein se kis mein right angle hai, aur kahan? (a) Sides 20 cm, 21 cm aur 29 cm. (b) Sides 7 cm, 8 cm aur 11 cm.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check
3 mein se 1
Ek triangle ki sides 9 cm, 40 cm aur 41 cm hain. Kaun sa statement true hai?
Answer dekho

Answer (B) Ismein 41 cm wali side ke saamne right angle hai.

92+402=81+1600=1681=412, isliye converse se 41 cm wali side ke saamne ka angle 90∘ hai. Pehle option ki tarah sides ko jodna yeh test nahi hai.

9.6 'If X then Y' kehne ke doosre tareeke

Rozmarra ki English mein ek hi 'if … then …' idea ko kehne ke kai tareeke hain. Table 9.3 ka har sentence bilkul wahi baat kehta hai jo agar koi number 10 ka multiple hai, to woh even hai.

Table 9.3'If X then Y' kehne ke chhah tareekeNCERT Ek Note · p. 5
PatternExample
Agar X, to Y (if … then).Agar koi number 10 ka multiple hai, to woh even hai.
X implies Y (X⇒Y).10 ka multiple hona even hona imply karta hai.
Y jab X (when).Koi number even hota hai jab woh 10 ka multiple ho.
Y jab bhi X (whenever).Koi number even hota hai jab bhi woh 10 ka multiple ho.
Har X, Y hai (every).10 ka har multiple even hai.
X tabhi jab Y (only if).Koi number 10 ka multiple tabhi hota hai jab woh even ho.

4/4Koi number 10 ka multiple tabhi hota hai jab woh even ho. Phir bhi X⇒Y.

Fig. 9.8Tiles sentence mein idhar-udhar jaati hain, lekin X hamesha condition hai aur Y result.

Do tiles, orange X tile jis par 'a multiple of 10' likha hai aur green Y tile jis par 'even' likha hai, baari-baari chaar sentence patterns mein rakhi jaati hain. Step 1: 'If X, then Y'. Step 2: tiles khisak kar 'Y when X' banati hain. Step 3: 'Every X is Y'. Step 4: 'X only if Y'. Har pattern ke neeche wahi line X implies Y dikhati hai, yaani tiles sentence mein idhar-udhar jaane par bhi matlab kabhi nahi badalta.

Aakhri pattern mein bahut log uljh jaate hain. 'X only if Y' (yaani tabhi jab) ka matlab yeh nahi hai: Y⇒X. Yeh kehta hai ki X kabhi bhi Y ke bina nahi hota, yaani X⇒Y. To converse banane se pehle sentence ko 'if … then …' form mein dobara likho, X aur Y pehchaano, aur sirf tab unhe swap karo.

Quick check
3 mein se 1
Dukaan band rehti hai jab public holiday hota hai. 'If X then Y' form mein likhne par X kya hai?
Answer dekho

Answer (B) public holiday hai

Yahan X = public holiday hai aur Y = dukaan band hai: agar public holiday hai, to dukaan band hai.
Recap

Summary aur key points

  1. Proposition aisa sentence hai jo ya to true ho ya false (Section 9.1).
  2. 'If X then Y' ka converse 'if Y then X' hai. 'Sides a, b, c wale triangle mein' jaisa scene set karne wala phrase nahi badalta (Example 5).
  3. 'X implies Y', 'X⇒Y', 'Y when X' aur 'every X is Y', sabka matlab 'if X then Y' hai (Section 9.6).
  4. Counterexample 'if' part ko true aur 'then' part ko false banata hai. Proposition ko false dikhane ke liye ek hi kaafi hai (Section 9.2).
  5. Bahut saare matching cases proof nahi bante: Fermat ke numbers paanch baar prime the aur phir fail ho gaye (Fermat ki kahani).
  6. Proposition aur uska converse dono true ho sakte hain, dono false ho sakte hain, ya ek true aur ek false (Table 9.2).
  7. Koi number perfect square hai if and only if uske factors ka count odd hai. Har direction ke liye apna argument chahiye (Section 9.3).
  8. Triangle mein equal angles ke saamne equal sides hoti hain, aur a2+b2=c2 hone par c ke saamne right angle banna hi hai: dono converses true hain (isosceles converse, Baudhāyana–Pythagoras converse).

Exercise Set 9.1

Practice · 22 questions

Practice questions answers ke saath (NCERT “Exercise Set 9.1”)

Questions 1 se 12 mein har ek ek proposition deta hai. Kuch 'if … then …' form mein nahi likhe gaye: pehle unhe dobara likho (Section 9.6 dekho). Converse likho, phir tay karo ki dono mein se kaun se statements true hain. Har true statement ke saath reason do aur har false ke saath counterexample. Questions 18 se 22 extra practice ke liye hain.

  1. Short answerEasyNCERT Exercise Set 9.1, Q1

    Agar ek transversal do parallel lines ko kaatta hai, to alternate interior angles equal hote hain.

    Solution dikhao

    AnswerConverse: agar ek transversal do lines ko kaatta hai aur equal alternate interior angles banata hai, to lines parallel hain.

    Converse: agar ek transversal do lines ko kaatta hai aur alternate interior angles equal hain, to dono lines parallel hain.

    Proposition: true. Parallel lines ke liye corresponding angles equal hote hain, aur har alternate interior angle ek corresponding angle ke barabar hota hai, kyunki vertically opposite angles equal hote hain.

    Converse: true. Agar alternate interior angles equal hain, to wahi vertically-opposite-angle wala step corresponding angles ke ek pair ko equal bana deta hai, aur jo lines transversal ke saath equal corresponding angles banati hain woh parallel hoti hain.

  2. Short answerEasyNCERT Exercise Set 9.1, Q2

    Agar koi triangle equilateral hai, to woh isosceles hai (uski kam se kam do sides equal hain).

    Solution dikhao

    AnswerConverse: agar koi triangle isosceles hai, to woh equilateral hai.

    Converse: agar koi triangle isosceles hai (uski kam se kam do sides equal hain), to woh equilateral hai.

    Proposition: true. Equilateral triangle ki teeno sides equal hoti hain, to unmein se do to pakka equal hain.

    Converse: false. 5 cm, 5 cm aur 8 cm sides wale triangle ki do sides equal hain lekin woh equilateral nahi hai.

  3. Short answerHardNCERT Exercise Set 9.1, Q3

    Ek triangle hai △ABC, jismein BE, B se altitude hai (yaani BE⊥AC) aur CF, C se altitude hai (yaani CF⊥AB). Proposition: agar AB=AC, to BE=CF.

    Fig. 9.9BE aur CF is triangle ki altitudes hain: △ABC.NCERT Fig. 9.1 · p. 5

    Ek triangle ABC jiska A upar hai aur B aur C neeche left aur right mein. B se ek dashed line side AC ko E par right angle par milti hai, aur C se ek dashed line side AB ko F par right angle par milti hai. Right-angle marks dono feet dikhate hain.

    Solution dikhao

    AnswerConverse: agar BE=CF, to AB=AC.

    Converse: altitudes BE aur CF wale △ABC mein, agar BE=CF, to AB=AC.

    △ABC ka area do tareekon se likho: base AC ke saath height BE hai, aur base AB ke saath height CF hai.

    12⋅AC⋅BE=12⋅AB⋅CFAC⋅BE=AB⋅CF

    Proposition: true. Agar AB=AC, to dono sides ko is common length se divide karo, BE=CF milega.

    Converse: true. Agar BE=CF, to dono sides ko is common length se divide karo, AC=AB milega.

    Converse ke liye ek aur raasta: right triangles BEC aur CFB ka hypotenuse BC common hai aur BE=CF hai, isliye woh RHS se congruent hain. Tab ∠C=∠B, aur equal angles ke saamne equal sides hoti hain.

  4. Short answerEasyNCERT Exercise Set 9.1, Q4

    Kisi bhi numbers k, x aur y ke liye: agar x=y, to kx=ky.

    Solution dikhao

    AnswerConverse: agar kx=ky, to x=y.

    Converse: agar kx=ky, to x=y.

    Proposition: true. Equal numbers ko same number se multiply karne par results equal aate hain.

    Converse: false. k=0, x=2, y=5 lo: tab kx=0=ky, lekin x≠y.

    Jab k≠0 ho, tab converse sahi hai: dono sides ko k se divide karo. Isiliye equation solve karte waqt tum dono sides ko sirf aise number se divide kar sakte ho jo zero na ho.

  5. Short answerMediumNCERT Exercise Set 9.1, Q5

    Positive integers a aur b ke liye: jab bhi dono perfect cubes hon, unka product ab bhi perfect cube hota hai.

    Solution dikhao

    AnswerConverse: agar ab perfect cube hai, to a aur b dono perfect cubes hain.

    'If … then …' form mein: agar a aur b perfect cubes hain, to ab perfect cube hai. Converse: agar ab perfect cube hai, to a aur b dono perfect cubes hain.

    Proposition: true. Agar a=m3 aur b=n3, to ab=m3n3=(mn)3.

    Converse: false. a=2 aur b=4 lo: ab=8=23 cube hai, lekin na 2 cube hai na 4.

  6. Short answerEasyNCERT Exercise Set 9.1, Q6

    Real numbers x aur y ke liye: agar x=y, to x4=y4.

    Solution dikhao

    AnswerConverse: agar x4=y4, to x=y.

    Converse: agar x4=y4, to x=y.

    Proposition: true. Equal numbers ki fourth powers equal hoti hain.

    Converse: false. x=2 aur y=−2 lo: x4=16=y4, lekin x≠y.

  7. Short answerMediumNCERT Exercise Set 9.1, Q7

    Real numbers x aur y ke liye: agar x=y, to x5=y5.

    Solution dikhao

    AnswerConverse: agar x5=y5, to x=y.

    Converse: agar x5=y5, to x=y.

    Proposition: true. Equal numbers ki fifth powers equal hoti hain.

    Converse: true. Maan lo x5=y5 hai lekin x≠y, jaise x<y. Agar 0≤x<y, to x<y ko khud se paanch baar multiply karne par x5<y5 milta hai.

    Agar x<0≤y, to x5 negative hai aur y5 nahi, isliye x5<y5. Agar x<y<0, to 0<−y<−x, isliye (−y)5<(−x)5, jiska matlab hai x5<y5.

    Har case x5<y5 deta hai, jo x5=y5 ke against hai. Isliye x=y.

  8. Short answerEasyNCERT Exercise Set 9.1, Q8

    Yahan se Question 12 tak n ek positive integer hai. 18 ka har multiple 3 se aur 6 se bhi divisible hai.

    Solution dikhao

    AnswerConverse: agar n 3 aur 6 dono se divisible hai, to n 18 se divisible hai.

    'If … then …' form mein: agar n 18 se divisible hai, to woh 3 aur 6 dono se divisible hai. Converse: agar n 3 aur 6 dono se divisible hai, to n 18 se divisible hai.

    Proposition: true. 18k=3×6k=6×3k.

    Converse: false. 6, 3 se aur 6 se divisible hai lekin 18 se nahi. (12 bhi chalega.)

  9. Short answerMediumNCERT Exercise Set 9.1, Q9

    Jab bhi n 45 se divisible ho, woh 5 se aur 9 se divisible hota hai.

    Solution dikhao

    AnswerConverse: agar n 5 aur 9 dono se divisible hai, to n 45 se divisible hai.

    'If … then …' form mein: agar 45, n ko divide karta hai, to 5 aur 9 dono n ko divide karte hain. Converse: agar n 5 aur 9 dono se divisible hai, to n 45 se divisible hai.

    Proposition: true. 45k=5×9k=9×5k.

    Converse: true. 9 se divisible hone ka matlab hai ki n ke prime factorisation mein 3×3 hai. 5 se divisible hone ka matlab hai ki usmein 5 hai, jo ek alag prime hai. Isliye usmein yeh sab hai: 3×3×5=45, aur 45, n ko divide karta hai.

  10. Short answerMediumNCERT Exercise Set 9.1, Q10

    Jab bhi kisi prime p ke liye n=p3 ho, n ke theek chaar factors hote hain.

    Solution dikhao

    AnswerConverse: agar n ke theek 4 factors hain, to n kisi prime number ka cube hai.

    'If … then …' form mein: agar kisi prime p ke liye n=p3, to n ke theek chaar factors hain. Converse: agar n ke theek 4 factors hain, to n kisi prime ka cube hai.

    Proposition: true. Agar n=p3 aur p prime hai, to uska ek hi prime factor p hai, isliye uske factors 1, p, p2 aur p3 hain: theek 4.

    Converse: false. 6 ke theek 4 factors (1,2,3,6) hain lekin woh cube nahi hai.

  11. Short answerMediumNCERT Exercise Set 9.1, Q11

    pqr form ka har number, jahan p, q aur r teen alag primes hain, theek aath factors rakhta hai.

    Solution dikhao

    AnswerConverse: agar n ke theek 8 factors hain, to n teen alag primes ka product hai.

    'If … then …' form mein: agar teen alag primes ke liye n=pqr, to n ke theek aath factors hain. Converse: agar n ke theek 8 factors hain, to n teen alag primes ka product hai.

    Proposition: true. Agar n=pqr, to har factor p, q, r mein se kuch ka product hai: 1,p,q,r,pq,pr,qr,pqr. Yeh 8 factors hain.

    Converse: false. 24=23×3 ke theek 8 factors (1,2,3,4,6,8,12,24) hain, lekin woh teen alag primes ka product nahi hai.

  12. Short answerMediumNCERT Exercise Set 9.1, Q12

    Jab n aur n+2 ka ek hi common factor 1 ho, to number n odd hota hai.

    Solution dikhao

    AnswerConverse: agar n odd hai, to n aur n+2 ka 1 ke alawa koi common factor nahi hai.

    'If … then …' form mein: agar n aur n+2 ka ek hi common factor 1 hai, to n odd hai. Converse: agar n odd hai, to n aur n+2 ka 1 ke alawa koi common factor nahi hai.

    Proposition: true. Agar n even hota, to n aur n+2 dono even hote, aur unka common factor 2 hota. Isliye n odd hi hona chahiye.

    Converse: true. n aur n+2 ka common factor d unke difference 2 ko bhi divide karta hai. Isliye d ya to 1 hai ya 2. Kyunki n odd hai, d≠2, isliye d=1.

  13. Short answerMediumNCERT Exercise Set 9.1, Q13

    Har claim kehta hai ki ek formula hamesha prime number deta hai. Har claim ko ek counterexample se todo.

    1. Har whole number n≥1 ke liye 6n+1 prime hai.

      Solution dikhao

      Answern=4 lene par milta hai 25=5×5.

      n=1,2,3 se 7, 13, 19 milte hain, sab prime, lekin n=4 lene par milta hai 25=5×5.

    2. Har whole number n≥0 ke liye n2+n+17 prime hai.

      Solution dikhao

      Answern=16 lene par milta hai 289=17×17.

      n=0 se 15 tak ki saari values prime hain, jisse claim safe lagta hai. Lekin n=16 lene par milta hai 256+16+17=289=17×17.

    3. Har whole number n≥1 ke liye 2n+3 prime hai.

      Solution dikhao

      Answern=5 lene par milta hai 35=5×7.

      n=1,2,3,4 se 5, 7, 11, 19 milte hain, sab prime, lekin n=5 lene par milta hai 32+3=35=5×7.

  14. Short answerMediumNCERT Exercise Set 9.1, Q14

    Har statement ka ek counterexample dhoondho.

    1. Kisi prime ko double karke 1 jodne par hamesha prime milta hai.

      Solution dikhao

      Answerp=7 se 15 milta hai.

      p=2,3,5 se 5, 7, 11 milte hain, sab prime. Lekin p=7 lene par aata hai 15=3×5, jo prime nahi hai.

    2. Har odd number n ke liye 3n+2 prime hai.

      Solution dikhao

      Answern=5 se 245 milta hai.

      n=1 se 5 aur n=3 se 29 milta hai, dono prime. Lekin n=5 lene par aata hai 243+2=245=5×49, jo prime nahi hai.

  15. Short answerMediumNCERT Exercise Set 9.1, Q15

    Yeh raha ek true statement: 12 se divisible har number 2 aur 6 dono se divisible hota hai.

    1. Samjhao ki yeh statement true kyun hai.

      Solution dikhao

      12 ka multiple hai 12k=2×6k=6×2k, isliye woh 2 se aur 6 se divisible hai.

    2. Ravi kehta hai: 'Jo number 2 aur 6 ke tests paas kar le, woh 12 se divisible hoga hi.' Kya Ravi sahi hai? Samjhao.

      Solution dikhao

      Nahi. Yeh test converse par tika hai, agar koi number 2 aur 6 se divisible hai, to woh 12 se divisible hai, jo false hai: 18 2 se aur 6 se divisible hai lekin 12 se nahi. Asal mein 6 ka har multiple pehle se even hota hai, isliye 2 check karne se kuch naya nahi milta.

    3. Kaun se do chhote divisibility tests milkar 12 ke liye sach mein kaam karte hain?

      Solution dikhao

      Answer3 se aur 4 se divisibility.

      3 aur 4 use karo. 4 se divisible number ke prime factorisation mein 2×2 hota hai, aur 3 se divisible mein 3. Saath milkar unmein aata hai 2×2×3=12. Yeh isliye kaam karta hai kyunki 3 aur 4 ka 1 ke alawa koi common factor nahi hai.

  16. Short answerMediumNCERT Exercise Set 9.1, Q16

    9 ka ek shortcut: koi number 9 se divisible theek tab hota hai jab uske digits ka sum 9 ka multiple ho. Is relationship ko do 'if … then …' sentences mein likho, batao ki har ek true hai ya nahi, aur unhe 7614 par check karo.

    Solution dikhao

    AnswerDono sentences true hain; number 9 se divisible hai if and only if uske digits ka sum 9 ka multiple hai.

    Agar koi number 9 se divisible hai, to uske digits ka sum 9 ka multiple hai. Iska converse: agar kisi number ke digits ka sum 9 ka multiple hai, to woh number 9 se divisible hai.

    Dono true hain, kyunki 10=9+1, 100=99+1, 1000=999+1 aur aise hi aage. Isliye kisi number aur uske digit sum mein hamesha 9 ke multiple ka fark hota hai: ek 9 ka multiple theek tab hai jab doosra ho.

    Dono saath mein: koi number 9 se divisible hai if and only if uske digits ka sum 9 ka multiple hai. Check: 7+6+1+4=18, jo 9 ka multiple hai, aur sach mein 7614=9×846.

  17. Short answerHardNCERT Exercise Set 9.1, Q17

    Uttarayan ke liye Ahmedabad ki ek kite-maker do bamboo sticks ko saath baandhti hai aur unke chaaron ends ke around ek string ghumaati hai. Sticks quadrilateral ke diagonals ban jaati hain aur string uski sides. Maan lo 'type K' quadrilaterals ki koi class hai jo woh banana chahti hai.

    Fig. 9.10Sticks ko right angles par cross karna: off-centre (ek kite) aur dono ke beech mein (ek rhombus).NCERT Fig. 9.2 · p. 7

    Do frames saath-saath. Har ek mein do bamboo sticks right angles par cross karti hain aur ek dashed string unke chaaron ends ko jodti hai. Left mein sticks chhoti stick ke beech mein lekin lambi stick ke beech se kaafi upar cross karti hain, jisse kite shape banti hai. Right mein sticks dono ke beech mein cross karti hain, jisse rhombus banta hai.

    1. Maan lo agar koi quadrilateral type K ka hai, to uske diagonals perpendicular hain. Kya use sticks right angles par hi baandhni padengi?

      Solution dikhao

      Haan. Har type-K quadrilateral ke diagonals perpendicular hote hain. Agar sticks kisi aur angle par cross karti hain, to frame type K ka ho hi nahi sakta.

    2. Isi property ke saath, kya unhe right angles par baandhna type K pakka karne ke liye kaafi hai?

      Solution dikhao

      Nahi. Property batati hai ki har type-K shape mein kya hota hai, yeh nahi ki perpendicular diagonals wali har shape type K ki hai; woh iska converse hota, jo humein diya hi nahi gaya. Jaise, agar type K ka matlab 'rhombus' hota, to sticks ko right angles par off-centre cross karne se kite banti hai, rhombus nahi (Fig. 9.10).

    3. Ab iske bajaay maan lo: agar kisi quadrilateral ke diagonals perpendicular hain, to woh type K ka hai. Kya ab sticks ko right angles par baandhna kaafi hai?

      Solution dikhao

      Haan. Perpendicular diagonals wala koi bhi quadrilateral type K ka hai, chahe sticks ki lengths kuch bhi hon aur woh kahin bhi cross karein.

    4. (c) wali property ke saath, kya sticks ka right angles par hona zaroori hai?

      Solution dikhao

      Zaroori nahi. Yeh property perpendicular diagonals ke liye type K ki guarantee deti hai, lekin doosri shapes ke baare mein kuch nahi kehti. Ho sakta hai kuch type-K quadrilaterals ke diagonals perpendicular na hon.

  18. Quick answerEasy

    Agar Ravi 90 se zyada score karta hai, to use A grade milta hai ka converse kaun sa sentence hai?

    Answer dekho

    Answer (C) Agar Ravi ko A grade milta hai, to woh 90 se zyada score karta hai.

    Converse dono parts ko swap karta hai aur kuch nahi badalta. Pehla option bina swap kiye dono parts mein 'not' jodta hai, aur doosra swap karke 'not' jodta hai; dono alag statements hain.
  19. Quick answerEasy

    Agar koi proposition false hai, to uska converse bhi false hi hoga.

    Answer dekho

    Answer Galat

    Example 4: 'equal perimeters ⇒ congruent' false hai, lekin uska converse 'congruent ⇒ equal perimeters' true hai.
  20. Quick answerEasy

    Aisa akela case jo proposition ke 'if' part ko true aur 'then' part ko false bana de, kehlata hai.

    Answer dekho

    Answer counterexample

    Proposition ko false dikhane ke liye ek counterexample kaafi hai.
  21. Short answerMedium

    Part 1 mein tumne yeh fact dekha tha ki semicircle mein bana angle right angle hota hai. Ise ek point P aur diameter AB wale circle ke baare mein 'if … then …' proposition ki tarah likho. Phir iska converse likho aur tay karo ki converse true hai ya nahi.

    Solution dikhao

    AnswerConverse: agar ∠APB=90∘, to P diameter AB wale circle par hai. Yeh true hai.

    Proposition: agar P diameter AB wale circle par koi point hai (A aur B ke alawa), to ∠APB=90∘.

    Converse: agar ∠APB=90∘, to P diameter AB wale circle par hai.

    Converse true hai. Right triangle APB mein circumcentre hypotenuse AB ka midpoint hota hai (Part 1, Chapter 5), isliye A, P aur B se guzarne wala circle bilkul diameter AB wala circle hi hai. Isliye P us par hai.

  22. Short answerMedium

    Rectangles ke baare mein aisa proposition do jo false ho aur jiska converse bhi false ho. Har verdict ko counterexample se support karo.

    Solution dikhao

    Answer'Same perimeter ⇒ same area' false hai, aur iska converse bhi.

    Proposition: agar do rectangles ka perimeter same hai, to unka area same hai. False: 2 cm by 8 cm rectangle aur 4 cm by 6 cm rectangle dono ka perimeter 20 cm hai, lekin unke areas 16 cm² aur 24 cm² hain.

    Converse: agar do rectangles ka area same hai, to unka perimeter same hai. False: 2 cm by 8 cm rectangle aur 4 cm by 4 cm square dono ka area 16 cm² hai, lekin unke perimeters 20 cm aur 16 cm hain.

Apna NCERT exercise question dhoondo

Hamare practice questions ncert.ai ke liye likhe gaye hain aur NCERT exercises ko follow karte hain. Apni textbook ke question se match karne wala question dhoondo; uska answer uske saath hai.

Tumhari NCERT textbook meinYahan practice question
NCERT Exercise Set 9.1, Q1Practice Q1
NCERT Exercise Set 9.1, Q2Practice Q2
NCERT Exercise Set 9.1, Q3Practice Q3
NCERT Exercise Set 9.1, Q4Practice Q4
NCERT Exercise Set 9.1, Q5Practice Q5
NCERT Exercise Set 9.1, Q6Practice Q6
NCERT Exercise Set 9.1, Q7Practice Q7
NCERT Exercise Set 9.1, Q8Practice Q8
NCERT Exercise Set 9.1, Q9Practice Q9
NCERT Exercise Set 9.1, Q10Practice Q10
NCERT Exercise Set 9.1, Q11Practice Q11
NCERT Exercise Set 9.1, Q12Practice Q12
NCERT Exercise Set 9.1, Q13Practice Q13
NCERT Exercise Set 9.1, Q14Practice Q14
NCERT Exercise Set 9.1, Q15Practice Q15
NCERT Exercise Set 9.1, Q16Practice Q16
NCERT Exercise Set 9.1, Q17Practice Q17

Quick check: MCQs

  1. 9.1 Propositions aur 'if … then …' form3 questions
  2. 9.2 Kya true proposition ka converse bhi true hota hai?3 questions
  3. Argument kis direction ko prove karta hai?3 questions
  4. 9.4 Chaar possible outcomes2 questions
  5. 9.5 Baudhāyana–Pythagoras theorem aur uska converse3 questions
  6. 9.6 'If X then Y' kehne ke doosre tareeke3 questions
Glossary · 8

Key terms (English + Hindi)

congruentसर्वांगसमsarvaangsam
Do figures congruent hoti hain jab ek ko doosri par exactly rakha ja sake: unki shape aur size same hoti hai.Chapter mein pehli baar yahan aaya →
converseविलोमvilom
Woh proposition jo 'if' part aur 'then' part ko swap karne se milta hai: 'if X then Y' ka converse 'if Y then X' hai.Chapter mein pehli baar yahan aaya →
counterexampleप्रत्युदाहरणpratyudaharan
Ek particular case jo proposition ke 'if' part ko true aur 'then' part ko false bana de. Proposition ko false dikhane ke liye ek counterexample kaafi hai.Chapter mein pehli baar yahan aaya →
factor pair
Do whole numbers jinka product diya gaya number ho, jaise 36 ke liye 4 aur 9. Pair mein ek number do baar bhi aa sakta hai, jaise 6×6 mein.Chapter mein pehli baar yahan aaya →
if and only ifयदि और केवल यदिyadi aur keval yadi
'X if and only if Y', jise X⇔Y, likhte hain, kehta hai ki proposition aur uska converse dono true hain.Chapter mein pehli baar yahan aaya →
implies
'X implies Y', jise X⇒Y, likhte hain, ka matlab wahi hai jo 'if X then Y' ka: jab bhi X true ho, Y bhi true hota hai.Chapter mein pehli baar yahan aaya →
perfect squareपूर्ण वर्गpoorn varg
Aisa whole number jo kisi whole number ko khud se multiply karne par mile, jaise 49=7×7.Chapter mein pehli baar yahan aaya →
propositionकथनkathan
Aisa sentence jo ya to true ho ya false, lekin dono nahi. '15, 4 ka multiple hai' jaisa false sentence bhi proposition hi hai.Chapter mein pehli baar yahan aaya →

Tum chapter ke end tak pahunch gaye