html extension with php

[coper]

I found the file to add that lines but still don't work.
Anyone knows how can I do to use php code inside a html file?
I can do it adding this to a htaccess file

Code:

<FilesMatch "\.(htm|html|php)$">
SetHandler application/x-httpd-php
</FilesMatch>

php works but I get Fatal error: Call to undefined function: mysql_connect()
And if the file has php extension I don't get that error.