We will use Mathematical induction to proove this. But here you dont just have to asume that its true for k and prove for k+1. Here we have to use the extended case of MI.

Assume is a statement that

Now show that , and is correct. (which infact is)

Now assume

, and are true.

i.e.

Now prove that is trure.

To proove

now

Now in a few step you can show that is true. hence proved.