document.write( "Question 740508: Determine the common ratio of a geometric series that has these partial sums: S4= -3.5, S5= -3.75, S6= -3.875.\r
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Algebra.Com's Answer #451623 by Ed Parker(21)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "S4= -3.5, S5= -3.75, S6= -3.875.\r\n" );
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document.write( "The sum of the first 5 terms S5 minus the sum\r\n" );
document.write( "of the first 4 terms S4 is the fifth term a5.  \r\n" );
document.write( "That is:\r\n" );
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document.write( "-3.75 = S5 = a1+a2+a3+a4+a5\r\n" );
document.write( "-3.5  = S4 = a1+a2+a3+a4 \r\n" );
document.write( "-----------------------------------\r\n" );
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document.write( "Subtract those equations term by term\r\n" );
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document.write( "-3.75 - (-3.5) = a5  \r\n" );
document.write( "   -3.75 + 3.5 = a5\r\n" );
document.write( "         -0.25 = a5\r\n" );
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document.write( "Similarly, the sum of the first 6 terms S6 \r\n" );
document.write( "minus the sum of the first 5 terms S5 is the \r\n" );
document.write( "sixth term a6. That is:\r\n" );
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document.write( "-3.875 = S6 = a1+a2+a3+a4+a5+a6\r\n" );
document.write( "-3.75  = S5 = a1+a2+a3+a4+a5 \r\n" );
document.write( "-----------------------------------\r\n" );
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document.write( "Subtract those equations term by term\r\n" );
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document.write( "-3.875 - (-3.75) = a6  \r\n" );
document.write( "   -3.875 + 3.75 = a6\r\n" );
document.write( "          -0.125 = a6\r\n" );
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document.write( "So we have found two consecutive terms of the geometric series.\r\n" );
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document.write( "a5 = -0.25\r\n" );
document.write( "a6 = -0.125\r\n" );
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document.write( "We can find the common ratio by dividing ANY term by the preceding \r\n" );
document.write( "term, so we can find the common ratio r by dividing the 6th term\r\n" );
document.write( "by the 5th term:\r\n" );
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document.write( "r = \"%28-0.125%29%2F%28-0.25%29\" = 0.5 \r\n" );
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document.write( "Edwin
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