Answer
{$-4,-2$}
Work Step by Step
Simplify. $ (x^2+6x)^{\frac{1}{3}}=-2$
Take cubic on both sides.
we have, $ (x^2+6x)=(-2)^3$
or, $x^2+6x+8=0$
After factorziation,we have
Thus, $(x+2)(x+4)=0$
Hence, we can conclude that $x=${$-4,-2$}