 These videos are going to cover spheres. We're going to talk about both surface area and volume of spheres. So first off, a sphere is all points that are a given distance from a point called its center, and we know a sphere as ball or a globe. So if this is the center of the sphere, what you will notice is that it has a radius and it also has something called a great circle. If you jump down here, the great circle has the same center as the sphere and the same radius, and I always think about the equator of the Earth as the great circle. So if I were to draw a circle around or within this sphere, that's what's considered the great circle. So surface area and volume of a sphere, when you are finding the surface area of a sphere, it is similar to area of a circle, but with a 4 in front of it. So the surface area of a sphere is 4 times pi times r squared. The volume of a sphere is four-thirds, 4 over 3, times pi times r to the third power because we're doing volume. So four-thirds pi r cubed. So those are the two formulas we're going to use to do the rest of the examples on this note sheet. Number one, we're finding the surface area of a sphere with a radius of three. So surface area of a sphere is 4 pi r squared, and so the radius is three. Three to the second power is nine. Nine times four is 36. So 36 36 pi square centimeters would be the surface area of that sphere. Remember the difference between surface area and volume? Surface area is what covers the sphere? Like if you were going to wrap it up versus volume, which is if you were going to fill it with something like liquid or some other material. Number three, we are finding the volume of a sphere with a radius of five. So this time we're using the volume formula, which is four-thirds times pi r to the third power. So we will use four-thirds times pi times five to the third power. And here we're going to leave it as a fraction. Five to the third power is 125, five times five times five. And if you think of this as 125 over one, and you multiply straight across, four times 125 is 500. But 500 is not divisible by three, so we're just going to leave it as 500 over three pi. And this time we're doing volume, so it would be cubic centimeters.