You've posted here before, so you should know the deal by now. But, guessing from the fact that you've shown no work here either, I suppose reading the rules (for the third time, yeah? ) ought to be in your very near future. The three basic steps of mathematical induction are;
Prove the statement for some base case (e.g. n = 1 for this problem)
Assume it's true for some k (This is the induction hypothesis)
Use the induction hypothesis to prove the statement also holds for k + 1
Now it's time for you to show us what you know and what you've done so far.... and go! Off to the races!