document.write( "Question 398083: Deret geometri 2+2^2+2^3+....+2^n=254, n=....? \n" ); document.write( "

Algebra.Com's Answer #282079 by Tatiana_Stebko(1539) $\"\"$ $\"About$

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sum of the n numbers in a geometric progression
\n" ); document.write( " $\"S=%28a%28r%5En-1%29%29%2F%28r-1%29\"$
\n" ); document.write( "a=2, r=2
\n" ); document.write( "S=254
\n" ); document.write( " $\"%282%282%5En-1%29%29%2F%282-1%29=254\"$
\n" ); document.write( " $\"2%5En-1=127\"$
\n" ); document.write( " $\"2%5En=128\"$
\n" ); document.write( " $\"2%5En=2%5E7\"$
\n" ); document.write( " $\"n=7\"$ \n" ); document.write( "

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