Prove the following by mathematical induction ( be sure to indicate clearly the basis step and the inductive step; also, in the inductive step, state...

Prove the following by mathematical induction (be sure to indicate clearly the basis step and the inductive step; also, in the inductive step, state clearly what you need to prove, and make that you are working from left to right):

            For all integers n greater than or equal to 1, 1+2+3+...+n = [n(n+1)]/2.