document.write( "Question 917875: I would be thankful if someone kindly help me with this problem:
\n" ); document.write( "In an AP 3,7,11,... find the value of n for which the sum of the first 2n terms will exceed the sum of first n terms by 155.
\n" ); document.write( "I tried solving it as follows:
\n" ); document.write( "S2n = Sn + 155
\n" ); document.write( "2n/2 {2(3) + (n-1)(4)} = n/2 {2(3) + (n-1)(4)} + 155
\n" ); document.write( "Proceeding further I finally got:
\n" ); document.write( "2n^2 + n -155 = 0
\n" ); document.write( "This equation does not give the value of n as whole number. \n" ); document.write( "
Algebra.Com's Answer #558053 by Edwin McCravy(20056)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "Your error is here:\r\n" );
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document.write( "2n/2 {2(3) + (n-1)(4)} \r\n" );
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document.write( "Should be\r\n" );
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document.write( "2n/2 {2(3) + (2n-1)(4)}\r\n" );
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document.write( "because you are finding the \"2n\"th term.\r\n" );
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document.write( "That way you get\r\n" );
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document.write( "6n^2 + n -155 = 0 instead of 2n^2 + n -155 = 0\r\n" );
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document.write( "which factors.\r\n" );
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document.write( "Edwin
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