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AP EAMCET · Maths · Binomial Theorem

The coefficient of \(x^3\) in the power series expansion of \(\frac{1+4 x-3 x^2}{(1+3 x)^3}\) is

  1. A -27
  2. B 27
  3. C 153
  4. D -153
Verified Solution

Answer & Solution

Correct Answer

(A) -27

Step-by-step Solution

Detailed explanation

The coefficient of \( x^k \) in \( (1+3x)^{-3} \) is \( (-1)^k \binom{3+k-1}{k} 3^k = (-1)^k \frac{(k+2)(k+1)}{2} 3^k \). Coefficient of \( x^3 \) in \( (1+4 x-3 x^2)(1+3 x)^{-3} \) is…