document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=208540>Question 208540</A>: <I><SPAN STYLE=\"word-break: break-all;\"> find the sum of the first n terms of each arithmetic series\r<BR>\n" );
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document.write( "n=18; a1=40, d=-7 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #158457 by </B><A HREF=/tutors/aboutme.mpl?userid=checkley77><B>checkley77(12844)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=checkley77><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=158457\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> First we need to find the last number in the 18 series.<BR>\n" );
document.write( "L=a+(n-1)D<BR>\n" );
document.write( "L=40+(18-1)-7<BR>\n" );
document.write( "L=40+17*-7<BR>\n" );
document.write( "L=40-119<BR>\n" );
document.write( "L=-49 this is the 18 th. number.<BR>\n" );
document.write( "Sum=n/2(a+L)<BR>\n" );
document.write( "Sum=18/2(40-79)<BR>\n" );
document.write( "Sum=9*39<BR>\n" );
document.write( "Sum=-351 ans. </SPAN>\n" );
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