May 2, 1991 ACOS 3

### NAME

acos, acosf - arc cosine function

### LIBRARY

Math Library (libm, -lm)

### SYNOPSIS

```double` acos(```double x`)
```float` acosf(```float x`)

### DESCRIPTION

The acos(``) and acosf(``) functions compute the principal value of the arc cosine of ```x` in the range [0],.

### RETURN VALUES

If |x|>1, acos(```x`) and acosf(```x`) set the global variable errno to EDOM.

### SEE ALSO

asin(3), atan(3), atan2(3), cos(3), cosh(3), math(3), sin(3), sinh(3), tan(3), tanh(3)

### STANDARDS

The acos(``) function conforms to ANSI X3.159-1989 (``ANSI C89'') .