It'd be a great idea if you didn't assume everybody understands your notation and define what os ...Fibonacci sequence or what!?

And use parentheses: you actually meant , so if your Fibonacci sequence is

, then and you have the base case.

Suppose truthness for , and take . The inductive hypotheses tells us that both terms in the RHS fulfill the equality, so:

...and now just rearrange these terms and use the definition of Fibonacci sequence...