Derivative of a radical of a sine:
Via the Scalar Multiple rule, we can treat this as .
We can go a step further and consider it as involving a power and apply the Power and Chain rules:
Using the derivative of the sine, we also have
Combining these results, we have
Finally, we substitute for u:
Note that the argument of the sine and cosine in the result is the same as the argument of the sine in the original problem.