Cosine

Cosine is a trigonometric function describing the ratio of the adjacent side to the hypotenuse in a right triangle. It is often abbreviated cos.

x values y values 0 1 π/2 0 π -1 3π/2 0 2π 1

2π radians is equivalent to one circle. The graph continues in that pattern.

Relation to secant

<math>\cos \theta = \sin \left(\frac{\pi}{2} - \theta \right) = \frac{1}{\sec \theta}\,</math>