# Trigonometry - Cosine, SOHCAHTOA

In continuing with my trig homework help series, this post will explain another of the basic trig functions, the cosine function.

Solving trigonometry problems that use the cosine function is extremely similar to the sine function explained in the last post. The cosine function relates an angle of a right angle triangle to the ratio of its adjacent side and the hypotenuse. The ADJACENT side to the angle is one of the sides that makes up the angle, but is not the HYPOTENUSE (the longest side of the triangle). Referring back to the same trig triangle we've been working with, it can be seen that side "a" is adjacent to angle B, and so:

CosB = a/c

In more general terms, CosB = adjacent/hypotenuse. We write "Cos" as the shorthand form of Cosine.

SOH CAH TOA helps us to remember the cosine function as well. The "CAH" term is short for "Cosine means Adjacent over Hypotenuse."

Take a look at the previous labeled trig triangle and see for yourself how the cosine function works. If you can do the sine function without problems, cosine shouldn't give you any difficulties either in your trig homework. Once again, it is absolutely important to understand the relative namings of the sides.

#### 1 comment:

1. Simply brilliant. Fundamental concepts explained in their simplest terms. Well done.