I am not clear what i need in Localsettings.php. I have texvc working as I run the test as per the read me with
texvc /home/wiki/tmp /home/wiki/math "y=x+2" iso-8859-1 "rgb 1.0 1.0 1.0"
(although not wit exact path as above) and that produce the png file as expected
$wgShowExceptionDetails = true;
wfLoadExtension( 'Math' );
$wgDefaultUserOptions['math'] = 'mathml';