Judging by your function, you are to find the derivative in , right?
So, you have to differentiate using the chain rule and the quotient rule. The numerator is a composition of the sine function and of the linear function (a function of a function). See:
(For lack of confusion, I will use 't' instead of 'x' as the dummy variable.)
Once those two are joined as a composition, then we get:
, or in your case .
This function is then divided by another, and that is why you need the quotient rule.
The chain rule shows us that:
Where, in your case, .
The derivative of in is:
You first differentiate the cosine and then the function inside and multiply the original, .
Then, by using the quotient rule:
In your case:
Maybe the expression can be simplified, but it looks nice either way =)
Good luck and remember the chain rule when you differentiate a composition of functions.