# Arccos(x) function

Arccos(x), cos-1(x), inverse cosine function.

### Arccos definition

The arccosine of x is defined as the inverse cosine function of x when -1≤x≤1.

When the cosine of y is equal to x:

cos y = x

Then the arccosine of x is equal to the inverse cosine function of x, which is equal to y:

arccos x = cos-1 x = y

Here cos-1 x means the inverse cosine and does not mean cosine to the power of -1.

For example:

arccos 1 = cos-1 1 = 0 rad = 0°