document.write( "Question 1107236: what is the value of 9^(1/3) x 9^(1/9) x 9^(1/27) x ...?\r
\n" ); document.write( "\n" ); document.write( "also is there a general formula in solving these types of question? thanks!
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Algebra.Com's Answer #722258 by KMST(5328)\"\" \"About 
You can put this solution on YOUR website!
You know that \"%289%5Ex%29%289%5Ey%29%289%5Ez%29=9%5E%28%28x%2By%2Bz%29%29\" .
\n" ); document.write( "So,
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\n" ); document.write( "\n" ); document.write( "because
\n" ); document.write( "\"1%2F3%2B1%2F9%2B1%2F27%2B%22...%22=1%2F2\"
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\n" ); document.write( "That sum is the sum of an infinite geometric sequence.
\n" ); document.write( "The \"formula\" for such a sum with a first term \"b\" and a common ratio \"r%3C1\" is
\n" ); document.write( "\"sum=b%2F%281-r%29\" .
\n" ); document.write( "In the case of the sum above, with \"b=1%2F3\" and \"r=1%2F3\" ,
\n" ); document.write( "\"sum=%221%2F3%22%2F%281-%221%2F3%22%29=%221%2F3%22%2F%222%2F3%22=1%2F2\" .
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\n" ); document.write( "There is no need to memorize formulas, if you can deduce them.
\n" ); document.write( "Consider the sum or \"n\" terms
\n" ); document.write( "\"S=b%2Bbr%2Bbr%5E2%2Bbr%5E3%2B%22...%22%2Bbr%5E%28n-1%29\" .
\n" ); document.write( "\"rS=br%2Bbr%5E2%2Bbr%5E3%2B%22...%22%2Bbr%5E%28n-1%29%2Bbr%5En\" , and
\n" ); document.write( "\"rS-S=br%5En-b\" --> \"%28r-1%29S=b%28r%5En-1%29\" --> \"S=b%28r%5En-1%29%2Fr-1\" .
\n" ); document.write( "If \"r%3C1\" , we might like to write it as
\n" ); document.write( "\"S=b%281-r%5En%29%2F%281-r%29\" ,
\n" ); document.write( "and as \"n\" approaches \"infinity\" , \"r%5En\" approaches \"0\" ,
\n" ); document.write( "and \"S\" approaches \"b%2F%281-r%29\" .
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