My differentiation problem is:
I get to:
=
But book answer says:
How do they get to that?
Your calculation of dy/dx is wrong. I assume you realise that you have to use the chain rule ....?
In which case, I suggest you go back and re-do the calculation - do every step and set out your work exectly like the examples in your textbook.
If you need more help, please show ALL steps of your calculation so that specific errors, if present, can be pointed out.