.BR acos ()
function calculates the arc cosine of \fIx\fP; that is
the value whose cosine is \fIx\fP.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
On success, these functions return the arc cosine of
.IR x
in radians; the return value is in the range [0,\ pi].
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
-.SH "CONFORMING TO"
+.SH CONFORMING TO
C99, POSIX.1-2001.
The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR asin (3),
.BR atan (3),
.BR atan2 (3),