Then you assume it's true for , for some , and from that, you try and derive the truth of that expression for .
So by assuming that is true (this is your induction hypothesis), you want to prove that:
The way you would do that is to say that:
using the induction hypothesis.
Now you want to show that the RHS is .
Match up what I've said above with what your text book says about proof by induction and try and work out the why of it rather than the what.