Hi I'm stuck on this question about functions.

I have attached the question. It is Q7.

I have done the first bit thats the simplify bit

but I can't do the hence show f(x)=etc. bit.

Also I'm stuck on the bit after that.

Thats the hence show a(subscript n)=2^n+5^n

Help with these two bits would be greatly appreciated.

Thanks in advance for replies.