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TS EAMCET · Maths · Binomial Theorem

If f(n) is the coefficient of xn in the expansion of (1+x)(1-x)n, then f(2021)=

  1. A -2019
  2. B 2020
  3. C 2021
  4. D -2022
Verified Solution

Answer & Solution

Correct Answer

(B) 2020

Step-by-step Solution

Detailed explanation

1+x1-xn=1-xn+x1-xn Coefficient of xn in 1+x1-xn=fn ⇒fn= Coefficient of xn in 1-xn+ Coefficient of xn-1 in 1-xn ⇒f2021=-12021 C20212021+-12020 C20202021 ⇒f2021=-1+2021 f2021=2020
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