`acos`

, `acosf`

---arc cosine#include <math.h> double acos(doublex); float acosf(floatx);

**Description**

`acos`

computes the inverse cosine (arc cosine) of the input value.
Arguments to `acos`

must be in the range -1 to 1.

`acosf`

is identical to `acos`

, except that it performs
its calculations on `floats`

.

**Returns**

If `x` is not between -1 and 1, the returned value is NaN
(not a number) the global variable `errno`

is set to `EDOM`

, and a
`DOMAIN error`

message is sent as standard error output.

You can modify error handling for these functions using `matherr`

.

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