Question

The sum of the co-efficients in the expansion of ${(1-2x+5x^2)}^n$ is $a$ and the sum of the co-efficients in the expansion of ${(1+x)}^{2n}$ is b then

• A. a=b
• B. $a=b^2$
• C. $a^2=b$
• D. ab=1

Answer 1

The correct option is A a=b

Substituting x=1, in the first case, we get
$(6-2{)}^n$
$4^n=a$ ..(i)
Substituting x=1, in the second case, we get
$2^{2n}$
$=4^n$
$=b$ ..(ii)
Hence from i and ii,
$a=b$.