Trigonometry is one of the most useful tools for solving elementary problems in Geometry. In this lesson, we shall talk about the definitions of the basic trigonometric functions, and express various quantities associated with a triangle in terms of them.
1. The sine, the cosine, and the tangent
2. The sine and the cosine laws
3. The half-angle formulæ
4. Heron's formula
5. The circumradius
6. The inradius
7. The exradii