Solve (2/5)^x=125/8

$$( \frac { 2 } { 5 } ) ^ { x } = \frac { 125 } { 8 }$$

Solve for x

$$x=-3$$

Steps Using Definition of Logarithm

Use the rules of exponents and logarithms to solve the equation.

$$\left(\frac{2}{5}\right)^{x}=\frac{125}{8}$$

Take the logarithm of both sides of the equation.

$$\log(\left(\frac{2}{5}\right)^{x})=\log(\frac{125}{8})$$

The logarithm of a number raised to a power is the power times the logarithm of the number.

$$x\log(\frac{2}{5})=\log(\frac{125}{8})$$

Divide both sides by \log(\frac{2}{5}).

$$x=\frac{\log(\frac{125}{8})}{\log(\frac{2}{5})}$$

By the change-of-base formula \frac{\log(a)}{\log(b)}=\log_{b}\left(a\right).

$$x=\log_{\frac{2}{5}}\left(\frac{125}{8}\right)$$

Solve for x (complex solution)

$$x=\frac{2\pi n_{1}i}{\ln(\frac{2}{5})}+\log_{\frac{2}{5}}\left(\frac{125}{8}\right)$$

$$n_{1}\in \mathrm{Z}$$