\(\left(3x+1\right)^3=-8\)
\(\Rightarrow\left(3x+1\right)^3=\left(-2\right)^3\)
\(\Rightarrow3x+1=-2\)
\(\Rightarrow3x=\left(-2\right)-1\)
\(\Rightarrow3x=-3\)
\(\Rightarrow x=\left(-3\right):3\)
\(\Rightarrow x=-1\)
Vậy \(x=-1.\)
Chúc bạn học tốt!