We've seen that multiple times. We also need to use the fact that the derivative of cosine of x is equal to negative sine of x. And the other way around, the derivative with respect to x of sine of x is equal to positive cosine of x. So using just that, we can actually evaluate this, or evaluate g prime of x. So pause the video and see if you can do it. So probably the most intimidating part of this, because we know the derivative of sine of x and cosine of x is this expression here, and we can just rewrite this, or simplify it a little bit, so it takes a form that you might be a little bit more familiar with. So, actually let me just do this on the side here.