Ta thấy: \(\left\{\begin{matrix}\left|x\right|^3\ge0\\\left|x\right|\ge0\end{matrix}\right.\)\(\Rightarrow\left\{\begin{matrix}-\left|x\right|^3\le0\\-\left|x\right|\le0\end{matrix}\right.\)
\(\Rightarrow-\left|x\right|^3-\left|x\right|\le0\)
\(\Rightarrow7-\left|x\right|^3-\left|x\right|\le7\)
\(\Rightarrow B\le7\)
Dấu "=" xảy ra khi \(x=0\)
Vậy \(Max_B=7\) khi \(x=0\)