I am kinda new to proof and can find it difficult sometimes. Can some help me to solves the following proofs.

1. d/dx (x^n)= nx^n-1

2. http://mathworld.wolfram.com/images/...dEquation4.gif r(r+1) = 1/3 n(n+1)(n+2)

3. 1.1!+ 2.2! + 3.3! +...+ n.n! = (n+1)!-1

Thanks