document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=877110>Question 877110</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Please help me, I don't understand I've tried it and came up with -1874571.4 but I know the answer is 714.5. Could you please show me the steps...<BR>\n" );
document.write( "*** Find the partial sum of the geometric series. S9 for 1000-400+160-64+... </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #529187 by </B><A HREF=/tutors/aboutme.mpl?userid=rothauserc><B>rothauserc(4718)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=rothauserc><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=rothauserc><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=529187\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> S9 = a +ar +ar^2 +ar^3 +ar^4 + .... +ar^9, where r is the common ratio<BR>\n" );
document.write( "S9 = a(1 - r^9) / (1 - r)<BR>\n" );
document.write( "We are given 1000 -400 +160 -64 +<BR>\n" );
document.write( "To find r, we divide the second term by the first<BR>\n" );
document.write( "r = -400 / 1000 = -2/5<BR>\n" );
document.write( "S9 = 1000(1 -(-2/5)^9) / (1 -(-2/5)<BR>\n" );
document.write( "S9 = 1000(1 -(-0.000262144)) / 1.4<BR>\n" );
document.write( "S9 = 1000 * 1.000262144 / 1.4<BR>\n" );
document.write( "S9 = 714.47296<BR>\n" );
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