Hi
Can someone look where i have made a mistake because it doesn't match the answers in the book.
1)
You must ALWAYS add to the integral or whatever, so that all can know with respect to what you're integrating. Here, I assume you're integrating wrt x (i.e., it must be ), and thus the following step is WRONG because you did NOT take as a constant, as you should...
If you're indeed integrating wrt x, here it must be , as written in your book.