Show that for all positiver integers n,

x[ (1+x)^n-1 + (1+x)^n-2 +...+ (1+x)^2 + (1+x) + 1 ] = (1+x)^n-1

ii) Hence show that for 1< and= k < and= n,

(n-1)C(k-1) + (n-2)C(k-2) + (n-3)C(k-3) + ... + (k-1)C(k-1) = nCk

is nCr (the combinations thing)

I can't do the second part. Help pls