document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=782030>Question 782030</A>: <I><SPAN STYLE=\"word-break: break-all;\"> My question was about arithmetic series.     Sn = -126, t1= -1, and tn = -20<BR>\n" );
document.write( "How do I determine n?<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #476229 by </B><A HREF=/tutors/aboutme.mpl?userid=mananth><B>mananth(16946)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=mananth><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/cgi-bin/show-face.mpl?user=mananth><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=476229\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Sn = -126, t1= -1, and tn = -20<BR>\n" );
document.write( "How do I determine n?\r<BR>\n" );
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document.write( "tn = a+(n-1)d\r<BR>\n" );
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document.write( "-20 =-1+(n-1)d<BR>\n" );
document.write( "-19=(n-1)d\r<BR>\n" );
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document.write( "Sn= n/2[2a+(n-1)d]\r<BR>\n" );
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document.write( "-126=n/2[2(-1)+(n-1)d]\r<BR>\n" );
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document.write( "substitute (n-1)d =-19\r<BR>\n" );
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document.write( "-252=n[-2-19)]\r<BR>\n" );
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document.write( "-252=n[-21]\r<BR>\n" );
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document.write( "-252/-21=n<BR>\n" );
document.write( "n=22 </SPAN>\n" );
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