Now, if you want to find the surface area for a circle, or if we want to find the area, I guess you could say, of a circle, we know that area is pi r squared. Now, for our semicircle, you're going to divide by two. So what's the radius going to be? So let me zoom in a little bit. So what is the radius of one of these semicircles going to be? So the radius, I could draw it like this. My best attempt to draw one of these things.