document.write( "Question 1202408: The third term of a geometric progression is nine times the first term. The sum of the first six terms is k times the sum of the first two terms. Find the value of k. \n" ); document.write( "
Algebra.Com's Answer #837223 by ikleyn(52928)\"\" \"About 
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\n" ); document.write( "The third term of a geometric progression is nine times the first term.
\n" ); document.write( "The sum of the first six terms is k times the sum of the first two terms. Find the value of k.
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document.write( "\"S%5B6%5D\" = \"a%5B1%5D\" + \"a%5B2%5D\" + \"a%5B3%5D\" + \"a%5B4%5D\" + \"a%5B5%5D\" + \"a%5B6%5D\".\r\n" );
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document.write( "Group the terms\r\n" );
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document.write( "\"S%5B6%5D\" = (\"a%5B1%5D+%2B+a%5B2%5D\") + (\"a%5B3%5D+%2B+a%5B4%5D\") + (\"a%5B5%5D+%2B+a%5B6%5D\").\r\n" );
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document.write( "You are given  \"a%5B3%5D\" = \"9%2Aa%5B1%5D\".\r\n" );
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document.write( "It implies  \"a%5B4%5D\" = \"9%2Aa%5B2%5D\";  \"a%5B5%5D\" = \"81%2Aa%5B1%5D\";  \"a%5B6%5D\" = \"81%2Aa%5B2%5D\".\r\n" );
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document.write( "Therefore\r\n" );
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document.write( "\"S%5B6%5D\" = \"%28a%5B1%5D+%2B+a%5B2%5D%29\" + \"9%2A%28a%5B1%5D+%2B+a%5B2%5D%29\" + \"81%2A%28a%5B1%5D+%2B+a%5B2%5D%29\" = \"%281+%2B+9+%2B+81%29%2A%28a%5B1%5D%2Ba%5B2%5D%29\" = \"91%2A%28a%5B1%5D%2Ba%5B2%5D%29\".\r\n" );
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document.write( "Thus the coefficient k is equal to 91.\r\n" );
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document.write( "ANSWER.  k = 91.\r\n" );
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\n" ); document.write( "\n" ); document.write( "On geometric progressions,  see introductory lessons\r
\n" ); document.write( "\n" ); document.write( "    - Geometric progressions\r
\n" ); document.write( "\n" ); document.write( "    - The proofs of the formulas for geometric progressions \r
\n" ); document.write( "\n" ); document.write( "    - Problems on geometric progressions\r
\n" ); document.write( "\n" ); document.write( "    - Word problems on geometric progressions\r
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\n" ); document.write( "\n" ); document.write( "Learn the subject from there.\r
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