# What is cos^-1(5/13)?

##### 1 Answer

Aug 18, 2015

#### Explanation:

This ratio gives us a Pythagorean triangle

with hypotenuse

Unfortunately this is not one of the standard triangles with a simple angle.

The only ways to solve it are by using a calculator, or trig tables, or an infinite series approximation.

This gives

Note that the same

Therefore adding