document.write( "Question 692570: An arithmetic series has a third term of 0. The sum of the first 15 terms is – 300. What is the first term? \n" ); document.write( "
Algebra.Com's Answer #427076 by MathTherapy(10552)\"\" \"About 
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\n" ); document.write( "\n" ); document.write( "An arithmetic series has a third term of 0. The sum of the first 15 terms is – 300. What is the first term?\r
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\n" ); document.write( "\n" ); document.write( "Formula for d, or the common difference in a series: \"d+=+%28a%5Bn%5D+-+a%5B1%5D%29%2F%28n+-+1%29\", with \"a%5Bn%5D\" = \"a%5B3%5D\" = 0, and n = 3\r
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\n" ); document.write( "\n" ); document.write( "Therefore, \"d+=+%28a%5Bn%5D+-+a%5B1%5D%29%2F%28n+-+1%29\" becomes: \"d+=+%280+-+a%5B1%5D%29%2F%283+-+1%29\" ------ \"d+=+%28-+a%5B1%5D%29%2F2\" ------ eq (i)\r
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\n" ); document.write( "\n" ); document.write( "Formula for sum of a series of numbers, or \"S%5Bn%5D\": \"S%5Bn%5D+=+%28n%2F2%29%282a%5B1%5D+%2B+%28n+-+1%29d%29\", with \"S%5Bn%5D\" = \"S%5B15%5D\" = - 300 ; and n = 15\r
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\n" ); document.write( "\n" ); document.write( "Therefore, \"S%5Bn%5D+=+%28n%2F2%29%282a%5B1%5D+%2B+%28n+-+1%29d%29\" becomes: \"S%5B15%5D+=+%2815%2F2%29%282a%5B1%5D+%2B+%2815+-+1%29d%29\" --- \"-+300+=+7.5%282a%5B1%5D+%2B+14d%29\" --- \"-+300+=+15a%5B1%5D+%2B+105d\" --- eq (ii)\r
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\n" ); document.write( "\n" ); document.write( "\"-+300+=+15a%5B1%5D+%2B+105%28%28-+a%5B1%5D%29%2F2%29\" ------ Substituting \"%28-+a%5B1%5D%29%2F2\" for d in eq (ii)\r
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\n" ); document.write( "\n" ); document.write( "\"-+300+=+15a%5B1%5D+%2B+52.5%28-+a%5B1%5D%29\"\r
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\n" ); document.write( "\n" ); document.write( "\"-+300+=+15a%5B1%5D+-+52.5a%5B1%5D\"\r
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\n" ); document.write( "\n" ); document.write( "\"-+37.5a%5B1%5D+=+-+300\"\r
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\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D\", or 1st term = \"%28-+300%29%2F-+37.5\", or \"highlight_green%288%29\"\r
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\n" ); document.write( "\n" ); document.write( "You can do the check!!\r
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\n" ); document.write( "\n" ); document.write( "Send comments and “thank-yous” to “D” at MathMadEzy@aol.com
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