This topic covers geometric concepts of circles and complementary and supplementary angles. This series of four lessons covers the circumference and area of a circle, as well as complementary, supplementary, and vertical angles.

The lessons introduce the student to the idea of pi, and give well-known approximations for it. Also, the properties of complementary and supplementary angles are discussed.

### Circumference of a Circle

In this lesson, the student is introduced to the definitions of circumference, radius, and diameter. Then, pi is defined as the ratio of the circumference to the diameter. The student sees that pi is a constant, and then is given various examples where they’re given either the diameter or radius and asked to find the circumference.

### Area of a Circle

In this lesson, the student is introduced to the formula of an area of a circle. The student is then shown a few examples where they are given the radius or diameter of a circle, and the area is found using the formula.

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