If I understand your problem right, you want to prove this property by mathematical induction(?):
I assume that you know how to do MI:
1. Prove for n = 1: is true.
2. Assume that is true.
3. Prove that the step from n to (n+1) is true under the assumption:
. Now we add which is possible because of the <= sign!
. Cancel out the equal factors:
Thus this property is true for all