Có: \(\left(\dfrac{2}{5}\right)^{13.x}=\left(\dfrac{8}{125}\right)^5\)
\(\Rightarrow\left(\dfrac{2}{5}\right)^{13.x}=\left[\left(\dfrac{2}{5}\right)^3\right]^5\)
\(\Rightarrow\left(\dfrac{2}{5}\right)^{13.x}=\left(\dfrac{2}{5}\right)^{15}\)
\(\Rightarrow13.x=15\)
\(\Rightarrow x=\dfrac{15}{13}\)