document.write( "Question 39435: Find a1 of arithmetic sequence from given information.
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Algebra.Com's Answer #24869 by AnlytcPhil(1806)\"\" \"About 
You can put this solution on YOUR website!
Find a1 of arithmetic sequence from given information.
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document.write( "a7 = -45 a15 = -77\r
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document.write( "Use the formula:\r
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document.write( "an = a1 + (n-1)d\r
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document.write( " a7 = a1 + (7-1)d\r
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document.write( "-45 = a1 + 6d\r
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document.write( " a15 = a1 + (15-1)d
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document.write( " -77 = a1 + 14d\r
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document.write( "So you have this system of equations:\r
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document.write( " -45 = a1 +  6d
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document.write( " -77 = a1 + 14d\r
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document.write( "Can you solve that system of equations?
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document.write( "If not post again.\r
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document.write( "a1 = -21, d = -4\r
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document.write( "Edwin
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document.write( "AnlytcPhil@aol.com  \n" );
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