document.write( "Question 719677: the next number or item in the sequence:2- 5 15 45 135 405 1215 \n" ); document.write( "

Algebra.Com's Answer #441452 by swincher4391(1107) $\"\"$ $\"About$

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Let $\"d_n\"$ be the common difference between numbers n and n+1.\r
\n" ); document.write( "\n" ); document.write( "First look at the common difference between each term:\r
\n" ); document.write( "\n" ); document.write( "5-2 = 3 <---d1
\n" ); document.write( "15-5 = 10 <----d2
\n" ); document.write( "45-15 = 30 <----d3
\n" ); document.write( "135 - 45 = 90 <---d4
\n" ); document.write( "405 - 135 = 270 <----d5
\n" ); document.write( "1215- 405 = 810 <----d6\r
\n" ); document.write( "\n" ); document.write( "Notice that $\"d_1+%2A+d_n\"$ gives $\"d_%28n%2B1%29\"$ .\r
\n" ); document.write( "\n" ); document.write( "So to find d7, we need to take 3 * 810 = 2430 which is the difference between 810 and the next number. So 2430 + 810 = 3240.\r
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