document.write( "Question 1047476: Question on Arithmetic Progression (AP)
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Algebra.Com's Answer #663038 by ikleyn(52790) $\"\"$ $\"About$

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\n" ); document.write( "Question on Arithmetic Progression (AP)
\n" ); document.write( "Find the S15 if T4 = 15 and T9 = 30
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document.write( "You are given \r\n" );
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document.write( "T4 = 15 = T1 + 3*d,   (1)\r\n" );
document.write( "T9 = 30 = T1 + 8*d.   (2)\r\n" );
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document.write( "Distract (1) from (2) and get 5d = 15,  d = 3.\r\n" );
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document.write( "Then from (1) find T1 = 15 - 3*d = 15 - 9 = 6.\r\n" );
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document.write( "So, your AP has the first term T1 = 6 and the common difference 3.\r\n" );
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document.write( "Now apply the formula for the sum of AP.\r\n" );
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\n" ); document.write( "\n" ); document.write( "For arithmetic progressions, see the lessons \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( "    - Chocolate bars and arithmetic progressions\r
\n" ); document.write( "\n" ); document.write( "    - Mathematical induction and arithmetic progressions\r
\n" ); document.write( "\n" ); document.write( "    - One characteristic property of arithmetic progressions\r
\n" ); document.write( "\n" ); document.write( "    - Mathematical induction for sequences other than arithmetic or geometric\r
\n" ); document.write( "\n" ); document.write( "    - Proving inequalities by the method of Mathematical Induction\r
\n" ); document.write( "\n" ); document.write( "    - Solved problems on arithmetic progressions \r
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\n" ); document.write( "\n" ); document.write( "OVERVIEW of these lessons on arithmetic progressions with short annotations is in the lesson OVERVIEW of lessons on arithmetic progressions.\r
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