document.write( "Question 1141644: If an = 3n + 4, find the sum of the first 20 terms in the sequence. \n" ); document.write( "
Algebra.Com's Answer #762230 by ikleyn(52788)\"\" \"About 
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document.write( "It is arithmetic progression with the first term \"a%5B1%5D\" = 7, the common difference d = 3 and the number of terms n = 20.\r\n" );
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document.write( "Use the formula for the sum of the first \"n\" terms of an AP\r\n" );
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document.write( "    \"S%5Bn%5D\" = \"%28a%5B1%5D+%2B+%28%28n-1%29%2Ad%29%2F2%29%2An\".\r\n" );
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document.write( "Substitute the given values into the formula\r\n" );
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document.write( "    \"S%5B20%5D\" = \"%287+%2B+%28%2820-1%29%2A3%29%2F2%29%2A20\".\r\n" );
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document.write( "Now use your calculator (or computer) to get the numerical value.\r\n" );
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document.write( "Do not forget to post your \"THANKS\" to me when you complete this assignment.\r\n" );
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\n" ); document.write( "\n" ); document.write( "For introductory lessons on arithmetic progressions see \r
\n" ); document.write( "\n" ); document.write( "    - Arithmetic progressions\r
\n" ); document.write( "\n" ); document.write( "    - The proofs of the formulas for arithmetic progressions \r
\n" ); document.write( "\n" ); document.write( "    - Problems on arithmetic progressions \r
\n" ); document.write( "\n" ); document.write( "    - Word problems on arithmetic progressions\r
\n" ); document.write( "\n" ); document.write( "in this site.\r
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\n" ); document.write( "\n" ); document.write( "Also,  you have this free of charge online textbook in ALGEBRA-II in this site\r
\n" ); document.write( "\n" ); document.write( "    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.\r
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\n" ); document.write( "\n" ); document.write( "The referred lessons are the part of this online textbook under the topic \"Arithmetic progressions\".\r
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\n" ); document.write( "\n" ); document.write( "Save the link to this textbook together with its description\r
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\n" ); document.write( "\n" ); document.write( "Free of charge online textbook in ALGEBRA-II
\n" ); document.write( "https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson\r
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\n" ); document.write( "\n" ); document.write( "into your archive and use when it is needed.\r
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