The coefficient of xn in the binomial expansion of 1-x-2 is
1-x-2=1+2x+3x2+..............+n+1xn+......
The coefficient of xn=n+1
Prove that the coefficient of xn in the binomial expansion of (1+x)2n is twice the coefficient of xn in the binomial expansion of (1+x)2n−1.