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) (x-a)^2 + (x-b)^2 =0
(C) (sin a)^2 + (cos b)^2 =1
(D) ab=1

Ans. A,B,C
But How???

Answer 1

It seems to me the values of a and b depend upon n.
If n = 0, a = b = 1
If n = 1, a = 4 and b = 4
if n = 2, a = 11 and b =16
Therefore none of the choices are true for all n.