Students will see a visual proof for the area formula of a circle, and two ways of proving the area formula using integrals. The visual proof and the first method are shown here. The second method is shown here. I would show students those methods in that order, as I consider the first method somewhat less complicated.

Conclude by giving your students these challenges:

- Number Rules - OK by NRICH
- Eight Dominoes by NRICH
- Shapely Pairs by NRICH
- Multiply the Addition Square by NRICH
- Intersecting Tetrahedra