Monday, February 4, 2013

Find the solution of the equation 5^(11x-1)=7^x

Since the bases are not matching, we can use logarithms to
solve exponential equations.


We'll take logarthims both
sides:


log5  [5^(11x-1)] = log5
(7^x)


We'll apply the power rule for
logarithms:


(11x-1) log5 5 = x log5
7


We'll recall that log5 5 =
1


We'll re-write the
equation:


11x-1 = x log5
7


We'll subtract x log5 7  both
sides:


11x - x log5 7 =
1


We'll factorize by x:


x(11 -
log5 7) = 1


We'll re-write log5 7 =
lg7/lg5


x(11 - lg7/lg5) =
1


We'll divide by 11 - lg7/lg5 =
9.7909


x = 1/9.7909


Rounded to
four decimal places:


x =
0.1021

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