Question

Tìm x, biết:

a/ \(\frac{5}{6}x-\frac{3}{8}x-10=12\)

b/ (/x/-1/8) . \(\left(-\frac{1}{8}\right)^5=\left(-\frac{1}{8}\right)^7\)

c/ \(3^x+3^{x+1}+3^{x+2}=117\)

Answer 1

a) \(\frac{5}{6}\)x - \(\frac{3}{8}\)x - 10 = 12

=> \(\left(\frac{5}{6}-\frac{3}{8}\right)\)x = 12 + 10

=> \(\frac{11}{24}\)x = 22

=> x = 22 : \(\frac{11}{24}\)

=> x = 48

Vậy x = 48.

b) (\(\left|x\right|\) - \(\frac{1}{8}\)) . \(\left(-\frac{1}{8}\right)^5\) = \(\left(-\frac{1}{8}\right)^7\)

=> \(\left|x\right|\) - \(\frac{1}{8}\) = \(\left(-\frac{1}{8}\right)^7\) : \(\left(-\frac{1}{8}\right)^5\)

=> \(\left|x\right|\) - \(\frac{1}{8}\) = \(\left(-\frac{1}{8}\right)^{7-5}\)

=> \(\left|x\right|\) - \(\frac{1}{8}\) = \(\frac{1}{64}\)

=> \(\left|x\right|\) = \(\frac{1}{64}\) + \(\frac{1}{8}\)

=> \(\left|x\right|\) = \(\frac{9}{64}\)

=> x = \(\frac{9}{64}\) hoặc x = \(\frac{-9}{64}\)

Vậy x = \(\frac{9}{64}\) hoặc x = \(\frac{-9}{64}\)

c) 3^x + 3^{x + 1} + 3^{x + 2} = 117 => 3^x (1 + 3 + 9) = 117 => 3^x . 13 = 117 => 3^x = 117 : 13 => 3^x = 9 => 3^x = 3² => x = 2 Vậy x = 2.