document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=104572>Question 104572</A>: <I><SPAN STYLE=\"word-break: break-all;\"> prove that:<BR>\n" );
document.write( "          Sum of n numbers in a sequence is n/2[2a+(n-1)d]. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #76099 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=76099\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> prove that:<BR>\n" );
document.write( "Sum of n numbers in a sequence is n/2[2a+(n-1)d].<BR>\n" );
document.write( "----------------<BR>\n" );
document.write( "Write the sequence          : S(n)=a        ,a+d         ,a+2d    ,.....a+(n-1)d<BR>\n" );
document.write( "Write the sequence backwards: S(n)=a+(n-1)d, a+(n-2d)    ,a+(n-3d)     ,a<BR>\n" );
document.write( "-----------------<BR>\n" );
document.write( "Add the two sequences to get: 2S(n)= n[a+a+(n-1)d]<BR>\n" );
document.write( "2S(n) = n[2a+(n-1)d]<BR>\n" );
document.write( "S(n) = (n/2)[2a+(n-1)d]<BR>\n" );
document.write( "============<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );