function writeHeader() {    // 
document.write('<table cellspacing="0" cellpadding="0" width="100%" border="0">');
document.write('<tr bgcolor="#666699"> ');
document.write('<td colspan="3" align="center"> ');
document.write('<img src="/math/images/entire_header_math.gif" width="586" height="137">');
document.write('</td></tr>');
}