1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.roff% 5.\" 6.\" @(#)acosh.3 8.1 (Berkeley) 06/04/93 7.\" 8.Dd 9.Dt ACOSH 3 10.Os BSD 4.3 11.Sh NAME 12.Nm acosh 13.Nd inverse hyperbolic cosine function 14.Sh SYNOPSIS 15.Fd #include <math.h> 16.Ft double 17.Fn acosh "double x" 18.Sh DESCRIPTION 19The 20.Fn acosh 21function computes the inverse hyperbolic cosine 22of the real 23argument 24.Ar x . 25For a discussion of error due to roundoff, see 26.Xr math 3 . 27.Sh RETURN VALUES 28The 29.Fn acosh 30function 31returns the inverse hyperbolic cosine of 32.Ar x . 33On the 34.Tn VAX 35and 36.Tn Tahoe , 37if the argument is less than one 38.Fn acosh 39sets the global variable 40.Va errno 41to 42.Er EDOM 43and 44causes a reserved operand fault. 45.Sh SEE ALSO 46.Xr asinh 3 , 47.Xr atanh 3 , 48.Xr exp 3 , 49.Xr infnan 3 50.Xr math 3 , 51.Sh HISTORY 52The 53.Fn acosh 54function appeared in 55.Bx 4.3 . 56