a) Ta có: 2x2 + 2x = 0
=> 2x(x + 1) = 0
=> \(\left[{}\begin{matrix}2x=0\\x+1=0\end{matrix}\right.\)
=> \(\left[{}\begin{matrix}x=0\\x=-1\end{matrix}\right.\)
Vậy x = 0 và x = -1 là nghiệm của đa thức 2x2 + 2x
b) Ta có: (x2 - 7)(x3 + x) = 0
=> \(\left[{}\begin{matrix}x^2-7=0\\x^3+x=0\end{matrix}\right.\)
=> \(\left[{}\begin{matrix}x^2=7\\x\left(x^2+1\right)=0\end{matrix}\right.\)
=> \(\left[{}\begin{matrix}\left[{}\begin{matrix}x=\sqrt{7}\\x=-\sqrt{7}\end{matrix}\right.\\\left[{}\begin{matrix}x=0\\x^2=-1\end{matrix}\right.\end{matrix}\right.\) (vì x2 \(\ge\)0)
=> \(\left[{}\begin{matrix}\left[{}\begin{matrix}x=\sqrt{7}\\x=-\sqrt{7}\end{matrix}\right.\\x=0\end{matrix}\right.\)
Vậy ...
