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Binomial Theorem question

2023 · 8 Apr · Shift 2 · Q23
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  5. /2023 · 8 Apr · Shift 2 · Q23

Binomial Theorem question

2023 · 8 Apr · Shift 2 · Q23

JEE MainMathematicsBinomial TheoremMCQ+4 / −1
25190−19190−8190+219025^{190}-19^{190}-8^{190}+2^{190}25190−19190−8190+2190 is divisible by :
  1. A
    14 but not by 34
  2. B
    neither 14 nor 34
  3. C
    both 14 and 34
  4. D
    34 but not by 14
View written solutionFree

Correct answer: D

  1. Let N=25190−19190−8190+2190.N=25^{190}-19^{190}-8^{190}+2^{190}.N=25190−19190−8190+2190. We need to check divisibility by 141414 and by 343434.

  2. Check divisibility by 141414. Since 14=2⋅714=2\cdot 714=2⋅7, it is enough to check modulo 777 because NNN is clearly even:

  • 2519025^{190}25190 is odd
  • 1919019^{190}19190 is odd
  • 81908^{190}8190 is even
  • 21902^{190}2190 is even So odd −-− odd −-− even +++ even === even.

Now reduce modulo 777: 25≡4(mod7),19≡5(mod7),8≡1(mod7),2≡2(mod7).25\equiv 4 \pmod 7,\quad 19\equiv 5 \pmod 7,\quad 8\equiv 1 \pmod 7,\quad 2\equiv 2 \pmod 7.25≡4(mod7),19≡5(mod7),8≡1(mod7),2≡2(mod7). Thus N≡4190−5190−1190+2190(mod7).N\equiv 4^{190}-5^{190}-1^{190}+2^{190}\pmod 7.N≡4190−5190−1190+2190(mod7). Now, 43=64≡1(mod7)⇒4190=43⋅63+1≡4,4^3=64\equiv 1\pmod 7 \Rightarrow 4^{190}=4^{3\cdot 63+1}\equiv 4,43=64≡1(mod7)⇒4190=43⋅63+1≡4, 5≡−2(mod7)⇒5190≡(−2)190=2190,5\equiv -2\pmod 7 \Rightarrow 5^{190}\equiv (-2)^{190}=2^{190},5≡−2(mod7)⇒5190≡(−2)190=2190, so those two terms cancel. Also, 23=8≡1(mod7)⇒2190=23⋅63+1≡2.2^3=8\equiv 1\pmod 7 \Rightarrow 2^{190}=2^{3\cdot 63+1}\equiv 2.23=8≡1(mod7)⇒2190=23⋅63+1≡2. Hence N≡4−2−1+2=3(mod7).N\equiv 4-2-1+2=3\pmod 7.N≡4−2−1+2=3(mod7). So NNN is not divisible by 777, hence not divisible by 141414.

  1. Check divisibility by 343434. Since 34=2⋅1734=2\cdot 1734=2⋅17, again NNN is even, so it remains to check modulo 171717.

Reduce modulo 171717: 25≡8(mod17),19≡2(mod17),8≡8(mod17),2≡2(mod17).25\equiv 8 \pmod{17},\quad 19\equiv 2 \pmod{17},\quad 8\equiv 8 \pmod{17},\quad 2\equiv 2 \pmod{17}.25≡8(mod17),19≡2(mod17),8≡8(mod17),2≡2(mod17). Therefore N≡8190−2190−8190+2190=0(mod17).N\equiv 8^{190}-2^{190}-8^{190}+2^{190}=0\pmod{17}.N≡8190−2190−8190+2190=0(mod17). So NNN is divisible by 171717. Since NNN is also even, it follows that NNN is divisible by 343434.

  1. Conclusion:
  • Not divisible by 141414
  • Divisible by 343434

Therefore the correct option is D: 34 but not by 14.\boxed{\text{D: 34 but not by 14}}.D: 34 but not by 14​.

  1. Comparison with stored answer: Stored correct answer is D, which matches our result.
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