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diff --git a/man3/tan.3 b/man3/tan.3
index 2dd1837228..6a0c3d966e 100644
--- a/man3/tan.3
+++ b/man3/tan.3
@@ -1,5 +1,8 @@
 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
+.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
+.\"     <mtk.manpages@gmail.com>
 .\"
+.\" %%%LICENSE_START(VERBATIM)
 .\" Permission is granted to make and distribute verbatim copies of this
 .\" manual provided the copyright notice and this permission notice are
 .\" preserved on all copies.
@@ -8,7 +11,7 @@
 .\" manual under the conditions for verbatim copying, provided that the
 .\" entire resulting derived work is distributed under the terms of a
 .\" permission notice identical to this one.
-.\" 
+.\"
 .\" Since the Linux kernel and libraries are constantly changing, this
 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
 .\" responsibility for errors or omissions, or for damages resulting from
@@ -16,9 +19,10 @@
 .\" have taken the same level of care in the production of this manual,
 .\" which is licensed free of charge, as they might when working
 .\" professionally.
-.\" 
+.\"
 .\" Formatted or processed versions of this manual, if unaccompanied by
 .\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
 .\"
 .\" References consulted:
 .\"     Linux libc source code
@@ -28,32 +32,127 @@
 .\" Modified 2002-07-27 by Walter Harms
 .\" 	(walter.harms@informatik.uni-oldenburg.de)
 .\"
-.TH TAN 3 2002-07-27 ""  "Linux Programmer's Manual"
+.TH TAN 3 2017-09-15 ""  "Linux Programmer's Manual"
 .SH NAME
 tan, tanf, tanl \- tangent function
 .SH SYNOPSIS
 .nf
 .B #include <math.h>
-.sp
+.PP
 .BI "double tan(double " x );
-.br
 .BI "float tanf(float " x );
-.br
 .BI "long double tanl(long double " x );
 .fi
-.sp
-Link with \-lm.
+.PP
+Link with \fI\-lm\fP.
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.PP
+.ad l
+.BR tanf (),
+.BR tanl ():
+.RS 4
+_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
+    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.RE
+.ad
 .SH DESCRIPTION
-The \fBtan\fP() function returns the tangent of \fIx\fP, where \fIx\fP is
+These functions return the tangent of
+.IR x ,
+where
+.I x
+is
 given in radians.
-.SH "CONFORMING TO"
+.SH RETURN VALUE
+On success, these functions return the tangent of
+.IR x .
+.PP
+If
+.I x
+is a NaN, a NaN is returned.
+.PP
+If
+.I x
+is positive infinity or negative infinity,
+a domain error occurs,
+and a NaN is returned.
+.PP
+If the correct result would overflow,
+a range error occurs,
+and the functions return
+.BR HUGE_VAL ,
+.BR HUGE_VALF ,
+or
+.BR HUGE_VALL ,
+respectively, with the mathematically correct sign.
+.\" I think overflow can't occur, because the closest floating-point
+.\" representation of pi/2 is still not close enough to pi/2 to
+.\" produce a large enough value to overflow.
+.\" Testing certainly seems to bear this out.  -- mtk, Jul 08
+.\"
+.\" POSIX.1 allows an optional underflow error;
+.\" glibc 2.8 doesn't do this
+.\" POSIX.1 an optional range error for subnormal x;
+.\" glibc 2.8 doesn't do this
+.SH ERRORS
+See
+.BR math_error (7)
+for information on how to determine whether an error has occurred
+when calling these functions.
+.PP
+The following errors can occur:
+.TP
+Domain error: \fIx\fP is an infinity
+.I errno
+is set to
+.B EDOM
+(but see BUGS).
+An invalid floating-point exception
+.RB ( FE_INVALID )
+is raised.
+.TP
+Range error: result overflow
+.\" Unable to test this case, since the best approximation of
+.\" pi/2 in double precision only yields a tan() value of 1.633e16.
+.\" .I errno
+.\" is set to
+.\" .BR ERANGE .
+An overflow floating-point exception
+.RB ( FE_OVERFLOW )
+is raised.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbw21 lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.BR tan (),
+.BR tanf (),
+.BR tanl ()
+T}	Thread safety	MT-Safe
+.TE
+.SH CONFORMING TO
+C99, POSIX.1-2001, POSIX.1-2008.
+.PP
+The variant returning
+.I double
+also conforms to
 SVr4, 4.3BSD, C89.
-The 
-.I float
-and
-.I "long double"
-variants are C99 requirements.
-.SH "SEE ALSO"
+.SH BUGS
+Before version 2.10, the glibc implementation did not set
+.\" http://sourceware.org/bugzilla/show_bug.cgi?id=6782
+.I errno
+to
+.B EDOM
+when a domain error occurred.
+.SH SEE ALSO
 .BR acos (3),
 .BR asin (3),
 .BR atan (3),