document.write( "Question 1039756: The third term of an arithmetic sequence is -12 and the seventb term is 8. What is the the sum of the first 10 terms? Please show me your solution. Thanks! Godbless\r
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Algebra.Com's Answer #654504 by Edwin McCravy(20056) $\"\"$ $\"About$

You can put this solution on YOUR website!

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document.write( "      ,       ,   -12 ,       ,       ,       ,    8  , ...\r\n" );
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document.write( "Let d be the common difference between terms, then\r\n" );
document.write( "we subtract d each time going to the left of -12, and\r\n" );
document.write( "we add d each time going to the right of -12.\r\n" );
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document.write( "-12-2d,  -12-d,   -12 , -12+d , -12+2d, -12+3d, -12+4d, ...\r\n" );
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document.write( "So -12+4d = 8 \r\n" );
document.write( "       4d = 20\r\n" );
document.write( "        d = 5\r\n" );
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document.write( "Then first term = a₁ = -12-2d = -12-2(5) = -12-10 = -22\r\n" );
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document.write( "  -22 ,   -17 ,   -12 ,   -7  ,   -2  ,    3  ,    8  ,    13 ,    18 ,   23  , ...\r\n" );
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document.write( "Checking: -22-17-12-7-2+3+8+13+18+23 = 5\r\n" );
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document.write( "Edwin

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