Returns the radian value of the arc cosine of a number. The arc cosine is the angle whose cosine is the specified number. The returned value is from 0 to pi.
float acos(float number)
number is the cosine of the angle, and must be from -1 to 1.
Example
acos(1)
Returns 0.
acos(-0.5)
Returns 2.0944 radians.
