The coefficient of x4 in ((1+x/1-x))2,|x|

Question

The coefficient of x4 in ((1+x/1-x))2,|x|<1, is (A) 4 (B) -4 (C) 10- 4 C 2 (D) 16

Tardigrade Admin · Accepted Answer

(1+x)2(1-x)-2 =(1+x2+2 x)(1-x)-2 Co-efficient of x 4= 5 C 4+ 3 C 2+2 4 C 3=16

Q. The coefficient of $x^{4}$ in $(\frac{1 + x}{1 - x})^{2}, ∣ x ∣ < 1$ , is