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. So e to the x times the derivative of the second expression. So times the derivative of cosine of x, is negative sine, negative sine of x. And it might be a little bit confusing because e to the x is its own derivative, but this right over here, you can view this as this was the derivative of e to the x, which happens to be e to the x.