#\(N\)
\(\left|2x+4\right|\ge0\) \(\left(\forall x\right)\)
\(\left(y+2\right)^2\ge0\left(\forall y\right)\)
`=> |2x+4|+(y+2)^2`\(\ge0\) (với mọi x, y)
`=>`\(\left\{{}\begin{matrix}\left|2x+4\right|=0\\\left(y+2\right)^2=0\end{matrix}\right.\)
`=>` \(\left\{{}\begin{matrix}2x+4=0\\y+2=0\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}2x=0-4\\y=0-2\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}2x=-4\\y=-2\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=-4\div2\\y=-2\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=-2\\y=-2\end{matrix}\right.\)
vậy, `x=-2, y=-2`
=>2x+4=0 và y+2=0
=>x=-2 và y=-2
