document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=213949>Question 213949</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The number of diagonals d in a polygon with n sides is given by the formula d=n^2-3n/2. If the polygon has 90 diagonals, how many sides does it have?  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #161669 by </B><A HREF=/tutors/aboutme.mpl?userid=HyperBrain><B>HyperBrain(694)</B></A><img src=\"/images/stars/stars-11.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=HyperBrain><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=161669\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Using the formula you've given,<BR>\n" );
document.write( "n^2-3n/2=90<BR>\n" );
document.write( "So,<BR>\n" );
document.write( "n^2-3n=n(n-3)=180=15(12); note that 12=15-3<BR>\n" );
document.write( "---<BR>\n" );
document.write( "So, the polygon has <u>15</u> sides. </SPAN>\n" );
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