Correct clog10 documentation (bug 19673) [committed]

[Joseph Myers <joseph@codesourcery.com>]

Bug 19673 reports that the documentation of clog10 is incorrect, both
failing to include the division by log (10) in the imaginary part and,
in the non-TeX version of the equation only, describing the LHS as log
rather than log10.

This patch fixes both issues.  Note: I think it's appropriate that the
LHS says log10 not clog10, and that the cexp and clog descriptions
referred to in a comment in that bug report similarly say exp and log;
this is a mathematical description not a literal C one.

Tested for x86_64.  Committed.

2016-11-01  Joseph Myers  <joseph@codesourcery.com>

	[BZ #19673]
	* manual/math.texi (Exponents and Logarithms): Correct description
	of clog10.

diff --git a/manual/math.texi b/manual/math.texi
index ccafb94..b4bb323 100644
--- a/manual/math.texi
+++ b/manual/math.texi
@@ -804,10 +804,10 @@ These functions return the base 10 logarithm of the complex value
 @var{z}.  Mathematically, this corresponds to the value
 
 @ifnottex
-@math{log (z) = log10 (cabs (z)) + I * carg (z)}
+@math{log10 (z) = log10 (cabs (z)) + I * carg (z) / log (10)}
 @end ifnottex
 @tex
-$$\log_{10}(z) = \log_{10}|z| + i \arg z$$
+$$\log_{10}(z) = \log_{10}|z| + i \arg z / \log (10)$$
 @end tex
 
 These functions are GNU extensions.

-- 
Joseph S. Myers
joseph@codesourcery.com