Returns the degree 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 180.
float acosd(float number)
number is the cosine of the angle, and must be from -1 to 1.
acosd(1)
Returns 0 degrees.
acosd(-0.5)
Returns 120 degrees.