I'm having trouble with differentiating this properly...

Let be a solution of ,

Show that for constants a, , the function

, satisfies .

I know I have to use chain rule, but I'm having trouble with the notation.

This is what I thought I should do:

Let , and

But for , I end up with

If the and weren't there, I could say it works for k = 1, but I don't think I can just make those notation just "disappear."

How do I write this out properly, so that the solution is verified?