Overview
The cosine function expresses the relationship between lengths of right triangle. Specifically, the cosine of an angle {% \theta %} is the ratio of the length of the adjacent side of the triangle divided by the length of the hypoteneuse.
Relationship to Circle
A particularly instructive way to understand the sine is to plot a circle with radius 1. A point is chosen on the circle, where the very far right point is assigned a {% \theta=0 %}. Then the sine is equal to the projection of the selected point on the y-axis.
Relevant Formulas
- {% cos(a + b) = cos (a) cos (b) - sin (a) sin (b) %}
- {% \displaystyle \frac{d \; cos(x)}{dx} = -sin(x) %}