Question

12*7^n/(7^(n-1)-7^(n+1))

Answer 1

7 ^ ( N - 1 ) - 7 ^ ( N + 1 ) = 7 ^ N * ( 7 ^ (-1) - 7 ^ 1 ) = 7 ^ N * ( 1/7 - 7 ) = 
= 7 ^ N * ( - 6/7 ) 
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( 12 * 7 ^ N) /( 7 ^ N * ( - 6/7 ) = 12 / ( - 6/7) = ( - 14 )