Ta có: \(\dfrac{-x+1}{-3}=\dfrac{9}{\left(-x+1\right)^2}\)
\(\Leftrightarrow\left(-x+1\right).\left(-x+1\right)^2=9.-3\)
\(\Leftrightarrow\left(-x+1\right)^3=-27\)
\(\Leftrightarrow\left(-x+1\right)^3=\left(-3\right)^3\)
\(\Rightarrow-x+1=-3\)
\(\Leftrightarrow-x=-3-1=-4\)
\(\Leftrightarrow x=4\)
Vậy: x=4