document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=632888>Question 632888</A>: <I><SPAN STYLE=\"word-break: break-all;\"> How do you work this out? I feel real stupid but it has been a long time for me. <BR>\n" );
document.write( "n(n-1)/2 = 21 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #398531 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=398531\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> n(n-1)/2 = 21<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "Multiply both sides by 2 to get:<BR>\n" );
document.write( "n(n-1) = 42<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Expand the left side<BR>\n" );
document.write( "n^2 - n = 42<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "Subtract 42 from both sides:<BR>\n" );
document.write( "n^2 - n - 42 = 0<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "Factor:<BR>\n" );
document.write( "(n-7)(n+6) = 0<BR>\n" );
document.write( "----<BR>\n" );
document.write( "n-7 = 0 or n+6 = 6<BR>\n" );
document.write( "n = 7 or n = -6<BR>\n" );
document.write( "=====================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( "=========================== </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );