document.write( "Question 994585: 1,7,13.....are in ap.can the sum of any terms be 175?justify \n" ); document.write( "
Algebra.Com's Answer #613637 by KMST(5328)\"\" \"About 
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For an AP (arithmetic progression or arithmetic sequence) with first term \"a%5B1%5D\" and common difference \"d\" ,
\n" ); document.write( "the sum of the first \"n\" terms is
\n" ); document.write( "\"%28a%5B1%5D%2Ba%5Bn%5D%29%2An%2F2\" or
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\n" ); document.write( "\n" ); document.write( "The sum of the first \"n\" terms cannot be 175.
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\n" ); document.write( "ONE APPROACH:
\n" ); document.write( "For the AP 1, 7, 13, ... , with \"system%28a%5B1%5D=1%2C+d=7-1=6%29\" ,
\n" ); document.write( "the sum of the first \"n\" terms is
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\n" ); document.write( "\"n%283n-2%29=175\"-->\"3n%5E2-2n=175\"-->\"3n%5E2-2n-175=0\"
\n" ); document.write( "The solution to that equation is not a valid \"n\" , because it is not an integer:
\n" ); document.write( " .
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\n" ); document.write( "ANOTHER APPROACH:
\n" ); document.write( "The sum of the first \"n\" terms would be \"%281%2Ba%5Bn%5D%29%2An%2F2=%28%281%2Ba%5Bn%5D%29%2F2%29%2An\"
\n" ); document.write( "That means that \"%281%2Ba%5Bn%5D%29%2F2\" and \"n\" are integers that multiply to yield \"175\" .
\n" ); document.write( "We know that \"%281%2Ba%5Bn%5D%29%2F2%3En\" ,
\n" ); document.write( "because \"%28a%5B1%5D%2Ba%5B2%5D%29%2F2=%281%2B7%29%2F2=8%2F2=4%3E2\" ,
\n" ); document.write( "and for each unit increase in \"n\" , \"%281%2Ba%5Bn%5D%29%2F2\" increases by \"d%2F2=6%2F2=3\" .
\n" ); document.write( "That makes the possible combinations of factors of \"175\" are
\n" ); document.write( "\"5%2A35=175\" , which would mean \"system%28n=5%2C1%2Ba%5Bn%5D%29%2F2=35%29\" , and
\n" ); document.write( "\"7%2A25=175\" , which would mean \"system%28n=7%2C1%2Ba%5Bn%5D%29%2F2=25%29\" .
\n" ); document.write( "Neither option works:
\n" ); document.write( "\"n=5\" means \"a%5Bn%5D=a%5B5%5D=1%2B4%2A6=1%2B24=25\" and \"%281%2Ba%5Bn%5D%29%2F2=%281%2Ba%5B5%5D%29%2F2=%281%2B25%29%2F2=13\" .
\n" ); document.write( "\"n=7\" means \"a%5Bn%5D=a%5B7%5D=1%2B6%2A6=1%2B36=37\" and \"%281%2Ba%5Bn%5D%29%2F2=%281%2Ba%5B7%5D%29%2F2=%281%2B37%29%2F2=19\" .\r
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\n" ); document.write( "\n" ); document.write( "A DIFFERENT INTERPRETATION OF THE PROBLEM:
\n" ); document.write( "The sum of \"n\" consecutive terms (not starting from \"a%5B1%5D=1\" ) could be \"175\" :
\n" ); document.write( "\"7%2B13%2B19%2B25%2B31%2B37%2B43=175\" .
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