Hello, guenchy!

This seems to be an Inducation problem.

Something like . . .

. . Prove by induction that: .

You've verified ..

You assumed

You added to both sides:

. .

Now we want to show that the right side is the right side of ,

. . which is: .

Simplify the left side . . . It's just algebra, isn't it?

. .

Factor: .

. . .. . . There!