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7^x + 7^(x - 1) = 5^x - 5^(x - 1)

7^x*(1 + 1/7) = 5^x*(1 - 1/5)

7^x*(8/7) = 5^x*(4/5)

(5/7)^x = (8/7)/(4/5)= (8/7)*(5/4) = 10/7

x*(log(5) - log(7)) = log(10) - log(7)

x = (log(10) - log(7))/(log(5) - log(7)) = -1,06

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