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Binomial Theorem question

2021 · 17 Mar · Shift 1 · Q37
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  5. /2021 · 17 Mar · Shift 1 · Q37

Binomial Theorem question

2021 · 17 Mar · Shift 1 · Q37

JEE MainMathematicsBinomial TheoremNumerical+4 / −1
If (2021)3762 is divided by 17, then the remainder is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 4

  1. We need the remainder when (2021)3762(2021)^{3762}(2021)3762 is divided by 171717.

  2. First reduce the base modulo 171717: 2021÷172021 \div 172021÷17 Since 17×118=2006,17 \times 118 = 2006,17×118=2006, we get 2021−2006=15.2021 - 2006 = 15.2021−2006=15. So, 2021≡15(mod17).2021 \equiv 15 \pmod{17}.2021≡15(mod17). Hence, 20213762≡153762(mod17).2021^{3762} \equiv 15^{3762} \pmod{17}.20213762≡153762(mod17).

  3. Now write 15≡−2(mod17)15 \equiv -2 \pmod{17}15≡−2(mod17). Therefore, 153762≡(−2)3762=23762(mod17)15^{3762} \equiv (-2)^{3762} = 2^{3762} \pmod{17}153762≡(−2)3762=23762(mod17) because 376237623762 is even.

  4. Use Fermat's little theorem: Since 171717 is prime and gcd⁡(2,17)=1\gcd(2,17)=1gcd(2,17)=1, 216≡1(mod17).2^{16} \equiv 1 \pmod{17}.216≡1(mod17). Now reduce the exponent modulo 161616: 3762=16⋅235+2.3762 = 16 \cdot 235 + 2.3762=16⋅235+2. So, 23762=(216)235⋅22≡1235⋅4≡4(mod17).2^{3762} = (2^{16})^{235} \cdot 2^2 \equiv 1^{235} \cdot 4 \equiv 4 \pmod{17}.23762=(216)235⋅22≡1235⋅4≡4(mod17).

  5. Therefore, the remainder is 4.\boxed{4}.4​.

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