Với mõi x,y ta có ;
\(\left\{{}\begin{matrix}\left(x+1\right)^{2018}\ge0\\\left(y+2\right)^{2020}\ge0\end{matrix}\right.\)
Mà \(\left(x+1\right)^{2018}+\left(y+2\right)^{2020}=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x+1\right)^{2018}=0\\\left(y+2\right)^{2020}=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+1=0\\y+2=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=-1\\y=-2\end{matrix}\right.\)
Lại có : \(A=3x^2y-4x^2y+1\)
\(\Rightarrow A=-x^2y+1\)
\(\Leftrightarrow A=-\left(-1\right)^2.\left(-2\right)+1\)
\(=-2+1=-1\)
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