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TS EAMCET · Maths · Binomial Theorem

The coefficient of \(x^n\) in \(\frac{1-2 x}{e^x}\) is :

  1. A \(\frac{(1+2 n)}{n !}\)
  2. B \((-1)^n \cdot \frac{(1+2 n)}{n !}\)
  3. C \((-1)^n \cdot \frac{(1-2 n)}{n !}\)
  4. D \((-1)^n \cdot \frac{(1+4 n)}{n !}\)
Verified Solution

Answer & Solution

Correct Answer

(C) \((-1)^n \cdot \frac{(1-2 n)}{n !}\)

Step-by-step Solution

Detailed explanation

\(\frac{1-2 x}{e^x}=(1-2 x) e^{-x}\) \(=(1-2 x)\left(1-x+\frac{x^2}{2 !}-\frac{x^3}{3 !}+\ldots\right.\) \(\left.+(-1)^n \frac{x^n}{n !}+\ldots\right)\) \(\therefore\) Coefficient of \(x^n\) in \(\frac{1-2 x}{e^x}=\frac{(-1)^n}{n !}-\frac{2(-1)^n}{(n-1) !}\)…