Areas of Semicircles and Quarter Circle

How Do You Find the Area of a Circle if You Know the Radius?

If you know the radius of a circle, you can use it to find the area of that circle. Just plug that value into the formula for the area of a circle and solve. Watch this tutorial to see how it's done!
What is the Formula for the Area of a Circle?

Did you know that you can figure out the formula for the area of a circle by first turning the circle into a parallelogram? It seems a little weird, but it really works! Watch this tutorial to see how it's done!