document.write( "Question 891783: The sum of how many terms of the series 3,-6,12, ....will be 513? \n" ); document.write( "

Algebra.Com's Answer #540029 by josgarithmetic(39618) $\"\"$ $\"About$

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That looks like geometric sequence, $\"r=-2\"$ .
\n" ); document.write( "The general sequence's term is $\"3%2A%28-2%29%5E%28n-1%29\"$ and n would be the index of the term.\r
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\n" ); document.write( "\n" ); document.write( "You can think of the sequence this way:
\n" ); document.write( "3, 3(-2)^1, 3(-2)^2, 3(-2)^3, 3(-2)^4,....3(-2)^n
\n" ); document.write( "This way showing the sequence uses indexing from 0 to n-1.
\n" ); document.write( "Sum of the first n terms is $\"highlight%283%28%281-%28-2%29%5En%29%2F%281-%28-2%29%29%29%29\"$ .
\n" ); document.write( "For reference, other than a good college algebra book, you can see http://en.wikipedia.org/wiki/Geometric_series. \n" ); document.write( "

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