And that's just because you're going to see that the derivative is going to be something different when we approach x is equal to zero from the left versus when we approach x is equal to zero from the right. And that's why they just took it out of there for us. So let's just figure out what that derivative is for all the other values of x. So f prime of x is equal to, so for x is less than zero, we're going to take the derivative of this first case. So the derivative of one is just zero. The derivative of negative two sine of x, well derivative of sine of x is just cosine of x. So it's going to be negative two cosine of x.