You need to prove that, for fixed , , and , the following holds:

. . . . .

I'm not sure why you're having trouble with the base case...? Just plug "1" in for "n":

. . . . .

...and:

. . . . .

Where did you get stuck?

Then you assume:

. . . . .

Then you work with the formula with n = k + 1:

. . . . .

You can use the assumption step to plug in for the first part:

. . . . .

Then see where that leads.

. . . . .