1.
\(Q=9-\left(x+2019\right)^2\)
Có: \(\left(x+2019\right)^2\ge0\forall x\)
\(\Rightarrow9-\left(x+2019\right)^2\le9\forall x\)
\(\Rightarrow Q\le9\forall x\\ \Rightarrow Q_{min}=9\)
\("="\Leftrightarrow\left(x+2019\right)^2=0\\ \Rightarrow x+2019=0\\ \Rightarrow x=-2019\).
2. Sửa đề: Tìm MIN của A=...
Có: \(\left\{{}\begin{matrix}\left|x-1004\right|\ge0\forall x\\\left|x+1003\right|\ge0\forall x\end{matrix}\right.\)
\(\Rightarrow\left|x-1004\right|+\left|x+1003\right|\ge0\forall x\)
\(\Rightarrow A\ge0\forall x\\ \Rightarrow A_{min}=0\)
\("="\Leftrightarrow\left\{{}\begin{matrix}\left|x-1004\right|=0\\\left|x+1003\right|=0\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x-1004=0\\x+1003=0\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x=1004\\x=-1003\end{matrix}\right.\)
