=====acos=====
Syntax:

<code>
    #include <cmath>
    double acos( double arg );
</code>
The acos() function returns the arc cosine of arg, which will be in the range
[0, pi]. arg should be between -1 and 1. If arg is outside this range, acos()
returns NAN and raises a floating-point exception.

C++ also provides the following overloaded forms:
<code>
    #include <cmath>
    float acos( float arg ); // same as acosf() in C99
    long double acos( long double arg ); // same as acosl() in C99
</code>

Related Topics: [[asin]], [[atan]], [[atan2]], [[cos]], [[cosh]], [[sin]], [[sinh]], [[tan]], [[tanh]]