RETURN VALUES
The acos and the acosf functions return the arc cosine in the range [0, pi] radians. If:
| x | > 1,
acos x raises an invalid exception and returns an NaN.
SEE ALSO
asin(3), atan(3), atan2(3), cos(3), cosh(3), fenv(3), math(3), sin(3), sinh(3), tan(3), tanh(3)
STANDARDS
