# Why is cos(pi) and cos (-pi) both equal to -1?

##### 3 Answers

One of the reasons is because

This means that

An example is the present case

A full circle is

They are both equal to

because

if viewed as a unit circle centered on the Cartesian origin

the

and, at halfway around the unit circle,

#### Answer:

This is what a cosine graph looks like. Since

#### Explanation:

graph{cos(x) [-4.76, 4.84, -2.64, 2.16]}