That's one of the most magical things in mathematics. One of the things that makes e so special. So u prime of x is still equal to e to the x. And v prime of x, we know is negative sine of x. And so what's this going to be equal to? Well this is going to be equal to the derivative of the first expression. So the derivative of e to the x, which is just e to the x, times the second expression, not taking its derivative, so times cosine of x plus the first expression, not taking its derivative.