public static double acos (double a)

Returns the arc cosine of a value; the returned angle is in the
range 0.0 through *pi*. Special case:

- If the argument is NaN or its absolute value is greater than 1, then the result is NaN.

The computed result must be within 1 ulp of the exact result. Results must be semi-monotonic.

`a` | the value whose arc cosine is to be returned. |

Diagram: Math