std::acos

From Cppreference

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Defined in header <cmath>
float       acos( float arg );
double      acos( double arg );
long double acos( long double arg );

Computes arc cosine of arg

[edit] Parameters

arg

-

floating point value

[edit] Return value

arc sine of arg in radians in the range of [0; π] radians.

Domain error occurs if arg is outside the range [-1.0; 1.0]. NAN is returned in that case.

[edit] See also

asin	computes arc sine (arcsin(x)) (function)
atan	computes arc tangent (arctan(x)) (function)
atan2	arc tangent, using signs to determine quadrants (function)
cos	computes cosine (cos(x)) (function)
acos(std::complex) (C++11)	computes arc cosine of a complex number (arccos(z)) (function template)
acos(std::valarray)	applies the function std::acos to each element of valarray (function template)