DARCCOS is the inverse cosine function. This function accepts a number between -1 and 1 inclusive and returns the angle from the range 0 through +pi that has that cosine.

DARCCOS is calculated similarly to the arcsine function and uses the following identity:

DARCCOS(x) = pi/2-DARCSIN(x)

The value of pi/2 is given under “Common Constants” later in this section.