document.write( "Question 936142: find the sum of the first 20 terms in the series 1,5,9,13,17... \n" ); document.write( "
Algebra.Com's Answer #569587 by MathTherapy(10556)\"\" \"About 
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document.write( "To determine the sum, use the formula for the sum of an AP, with number of terms, 1st term, and common difference (d), known.
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document.write( "Formula: \"S%5Bn%5D+=+%28n%2F2%29%282a%5B1%5D+%2B+%28n+-+1%29d%29\"
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document.write( "\"S%5Bn%5D+=+%2820%2F2%29%282%281%29+%2B+%2820+-+1%294%29\" ------ Substituting 20 for n, 1 for \"a%5B1%5D\", and 4 for common difference , or d
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document.write( "\"S%5Bn%5D+=+10%282+%2B+%2819%294%29\"
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document.write( "\"S%5Bn%5D+=+10%282+%2B+76%29\"
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document.write( "\"S%5Bn%5D+=+10%2878%29\"
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document.write( "Sum of 1st 20 terms, or \"highlight_green%28S%5Bn%5D+=+780%29\" \n" );
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