7.12.4.1 The acos functions

Synopsis

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#include <math.h>
double acos(double x);
float acosf(float x);
long double acosl(long double x);

Description

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The acos functions compute the principal value of the arc cosine of x. A domain error occurs for arguments not in the interval [-1, +1].

Returns

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The acos functions return arccos x in the interval [0, pi ] radians.