1.

Prove that `: ""^(n)C_(0).""^(2n)C_(n)-""^(n)C_(1).""^(2n-2)Cn_(n)+""^(n)C_(2).""^(2n-4)Cn_(n)+......=2^n`

Answer» L.H.S = coefficent of `x^n "in" [""^(n)C_(0)(1+x)^(20)-""^(n)C_(1)(1+x)^(2n-2)....]`
= cofficient of `x^(n)[(1+x)^2-1]^n`
Coffficient of `x^n "in" x^n(X+2)^n=2^n`


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