The goal of this section is to prove that all circles are similar, use trigonometric ratios for special triangles (30-60-90 and 45-45-90), explain the relationship between sine and cosine, and define the the area of a sector.

A special right triangle is a right triangle with some regular feature that makes calculations on the triangle easier. For example, a right triangle may have angles that from a relationship such as a 45-45-90 triangle, also called an angle- bases right triangle.