a, Ta có \(\left(x+5\right)^2=16\)
Mà \(16=4^2=\left(-4\right)^2\)
\(\Rightarrow\left[{}\begin{matrix}x+5=-4\\x+5=4\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-4-5\\x=4-5\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-9\\x=-1\end{matrix}\right.\)
Vậy \(x\in\left\{-9;-1\right\}\)
b, Ta có \(\left(2x+5\right)^3=8\)
\(\Rightarrow\left(2x+5\right)^3=2^3\)
\(\Rightarrow2x+5=2\)
\(\Rightarrow2x=-3\)
\(\Rightarrow x=\dfrac{-3}{2}\)
Vậy \(x=\dfrac{-3}{2}\)
