The Cosine Function

The cosine of an angle is the ratio of the adjacent side to the hypotenuse of a right triangle. The hypotenuse is the side directly across from the right triangle. It is also the longest side of a right triangle. The side adjacent is the side touching the angle of interest other than the hypotenuse. The angle of interest is 29 degrees in figure one. Therefore, the side adjacent is the horizontal side of the triangle. Figure two shows the same triangle as figure one. The angle of interest is 61 degrees. Now the adjacent side is the vertical side of the triangle. Click on “Examples” to see how the cosine function is used to solve right triangle problems. Cosine is often abbreviated “Cos”.

*cos of a degree° =**adjacent/hypotenuse **Plug in, cross multiply and solve