Area of a Circle
A circle is round, so its area is hard to measure directly, but slice it like a pizza and fit the pieces together and the shape approaches a rectangle. That rectangle has a base of half the circumference and a height of the radius, so the area is radius times radius times pi. A pizza, a clock, and a coin are the everyday sizes this formula measures. Add slices and the circle opens into a rectangle that fills about 78.5% of the surrounding square.