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.TH acos 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions"
.SH NAME
acos, acosf, acosl \- arc cosine functions
.SH SYNOPSIS
.LP
.nf
c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ]
#include <math.h>

\fBdouble\fR \fBacos\fR(\fBdouble\fR \fIx\fR);
.fi

.LP
.nf
\fBfloat\fR \fBacosf\fR(\fBfloat\fR \fIx\fR);
.fi

.LP
.nf
\fBlong double\fR \fBacosl\fR(\fBlong double\fR \fIx\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions compute the principal value of the arc cosine of \fIx\fR. The
value of \fIx\fR should be in the range [\(mi1,1].
.SH RETURN VALUES
.sp
.LP
Upon successful completion, these functions return the arc cosine of \fIx\fR in
the range [0, \c
.if n pi\c
.if t \(*p
\c
] radians.
.sp
.LP
For finite values of  \fIx\fR not in the range [\(mi1,1], a domain error occurs
and NaN is returned.
.sp
.LP
If \fIx\fR is NaN, NaN is returned.
.sp
.LP
If \fIx\fR is +1, +0 is returned.
.sp
.LP
If \fIx\fR is \(+-Inf, a domain error occurs and NaN is returned.
.sp
.LP
For exceptional cases, \fBmatherr\fR(3M) tabulates the values to be returned by
\fBacos()\fR as specified by SVID3 and XPG3.
.SH ERRORS
.sp
.LP
These functions will fail if:
.sp
.ne 2
.mk
.na
\fBDomain Error\fR
.ad
.RS 16n
.rt  
The \fIx\fR argument is finite and not in the range [-1,1], or is \(+-Inf.
.sp
If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is
non-zero, the invalid floating-point exception is raised.
.sp
The \fBacos()\fR function sets \fBerrno\fR to \fBEDOM\fR if \fIx\fR is not
\(+-Inf or NaN and is not in the range [\(mi1,1].
.RE

.SH USAGE
.sp
.LP
An application wanting to check for exceptions should call
\fBfeclearexcept\fR(\fBFE_ALL_EXCEPT\fR) before calling these functions. On
return, if \fBfetestexcept\fR(\fBFE_INVALID\fR | \fBFE_DIVBYZERO\fR |
\fBFE_OVERFLOW\fR | \fBFE_UNDERFLOW\fR) is non-zero, an exception has been
raised. An application should either examine the return value or check the
floating point exception flags to detect exceptions.
.sp
.LP
An application can also set \fBerrno\fR to 0 before calling \fBacos()\fR. On
return, if \fBerrno\fR is non-zero, an error has occurred. The \fBacosf()\fR
and \fBacosl()\fR functions do not set \fBerrno\fR.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
Interface StabilityStandard
_
MT-LevelMT-Safe
.TE

.SH SEE ALSO
.sp
.LP
\fBcos\fR(3M), \fBfeclearexcept\fR(3M), \fBfetestexcept\fR(3M),
\fBisnan\fR(3M), \fBmath.h\fR(3HEAD), \fBmatherr\fR(3M), \fBattributes\fR(5),
\fBstandards\fR(5)