document.write( "Question 1055154: The sum of the second and the third terms of a geometric progression is 6,the sum of the third and the fourth term is -12.find;
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Algebra.Com's Answer #670493 by Edwin McCravy(20056) $\"\"$ $\"About$

You can put this solution on YOUR website!

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document.write( "The solution above contains an error. He took \r\n" );
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document.write( "\"The sum of the second and the third terms\"\r\n" );
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document.write( "as if it were\r\n" );
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document.write( "\"The sum of the FIRST and the third terms\"\r\n" );
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document.write( "The sum of the second and the third terms of a \r\n" );
document.write( "geometric progression is 6,\r\n" );
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document.write( "the sum of the third and the fourth term is -12.\r\n" );
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document.write( "Set the two expressions for a₁ equal:\r\n" );
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document.write( "Divide both sides by 6\r\n" );
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document.write( "Cross-multiply\r\n" );
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document.write( "Factor out r:\r\n" );
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document.write( "Factor the expression in parentheses:\r\n" );
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document.write( "Use zero-factor property.  Set each\r\n" );
document.write( "factor = 0:\r\n" );
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document.write( " r = 0;  r+1 = 0;  r+2 = 0\r\n" );
document.write( "          r = -1     r = -2\r\n" );
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document.write( "So we have three potential values for r:\r\n" );
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document.write( "If we use r = 0\r\n" );
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document.write( "Substitute in \r\n" );
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document.write( "That's undefined so we must discard r = 0\r\n" );
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document.write( "----\r\n" );
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document.write( "If we use r = -1\r\n" );
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document.write( "Substitute in \r\n" );
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document.write( "That's also undefined. So we must also discard r = -1\r\n" );
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document.write( "If we use r = -2\r\n" );
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document.write( "Substitute in \r\n" );
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document.write( "So the first term is 3,\r\n" );
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document.write( "The sequence = 3, -6, 12, -24, 48, -96, ...\r\n" );
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document.write( "The sum of the first 20 terms:\r\n" );
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document.write( "Edwin

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