document.write( "Question 754618: A1= 7, An= -20, Sn = -65 determine n and d. \n" ); document.write( "
Algebra.Com's Answer #459231 by tommyt3rd(5050)\"\" \"About 
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\"%0D%0AS%5Bn%5D=%28n%2F2%29%28a%5B1%5D%2Ba%5Bn%5D%29%0D%0A\"\r
\n" ); document.write( "\n" ); document.write( "so that\r
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\n" ); document.write( "\n" ); document.write( "\"%0D%0A-65=%28n%2F2%29%287%2B%28-20%29%29%0D%0A\"\r
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\n" ); document.write( "\n" ); document.write( "Therefore\r
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\n" ); document.write( "\n" ); document.write( "n=10\r
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\n" ); document.write( "\n" ); document.write( "As for the common difference\r
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\n" ); document.write( "\n" ); document.write( "\"%0D%0Ad=%28a%5Bn%5D-a%5B1%5D%29%2F%28n-1%29=%28-20-7%29%2F%2810-1%29=-3%0D%0A\"\r
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