Legacy Document

cos

You can use the cos function to compute the cosine of a real number.

double_t cos (double_t x);

x

Any finite floating-point number.

DESCRIPTION

The cos function returns the cosine of its argument. The argument is the measure of
an angle expressed in radians. This function is symmetric with respect to the y-axis
(cos x = cos -x).

The acos function performs the inverse operation $(arccos(y))$ .

EXCEPTIONS

When x is finite and nonzero, $cos(x)$ raises the inexact exception.

SPECIAL CASES

Table 10-20 shows the results when the argument to the cos function is a zero, a NaN, or an Infinity, plus other special cases for the cos function.

Special cases for the cos function

Operation	Result	Exceptions raised
$cos(pi)$	-1	Inexact
$cos(+0)$	1	None
$cos(-0)$	1	None
$cos(NaN)$	NaN	None[41]
$cos(+$ )	NaN	Invalid
$cos(-$ )	NaN	Invalid

EXAMPLES

z = cos(0);    /* z = 1.0. */
z = cos(pi/2); /* z = -0.0. The inexact exception is raised. */
z = cos(pi);   /* z = -1.0. The inexact exception is raised. */
z = cos(-pi/2);/* z = 0.0. The inexact exception is raised. */
z = cos(-pi);  /* z = -1.0. The inexact exception is raised. */

---

[41] If the NaN is a signaling NaN, the invalid exception is raised.