I think you're forgetting the product rule in a place or two. Also, your 's and 's are too much alike. Try this:
See what that does for you.
I am having difficulty expanding this exercise.
My attempt involved as attached but the next line of derivation has 3 more terms...I thought it was just a matter of multiplying out terms and simplifying...?
The answer is
Just one question. On the last line, could'nt we change the partial to ordinary derivatives because we have pulled out all the constants etc.
Ok, I will reply with results when I can... Thanks Ackbeet!!