Tìm x,y biết: (x - 2021)2 + (y + 2022)2 = 0
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Có: \(\left|2022-2x+y\right|\ge0\forall x,y\)
\(\left(x-y-2021\right)^2\ge0\forall x,y\)
\(\Rightarrow\left|2022-2x+y\right|+\left(x-y-2021\right)^2\ge0\forall x,y\)
Mặt khác: \(\left|2022-2x+y\right|+\left(x-y-2021\right)^2=0\)
nên \(\left\{{}\begin{matrix}2022-2x+y=0\\x-y-2021=0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}-2x+y=-2022\\x-y=2021\end{matrix}\right.\)
\(\Rightarrow-2x+y+x-y=-2022+2021\)
\(\Rightarrow-x=-1\Leftrightarrow x=1\)
Khi đó: \(1-y=2021\) \(\Leftrightarrow y=-2020\)
\(\Rightarrow x+y=1-2020=-2019\)
|2022-2x+y|+(x-y-2021)^2=0
=>2022-2x+y=0 và x-y-2021=0
=>x-y=2021 và 2x-y=2022
=>x=1 và y=-2020
\(\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}=\dfrac{1}{2022}\)
\(\Rightarrow\dfrac{yz+zx+xy}{xyz}=\dfrac{1}{x+y+z}\)
\(\Rightarrow\left(yz+zx+xy\right)\left(x+y+z\right)=xyz\)
\(\Rightarrow xy\left(x+y\right)+yz\left(y+z\right)+zx\left(z+x\right)+3xyz-xyz=0\)
\(\Rightarrow xy\left(x+y\right)+yz\left(y+z\right)+zx\left(z+x\right)+2xyz=0\)
\(\Rightarrow\left(x+y\right)\left(y+z\right)\left(z+x\right)=0\)
\(\Rightarrow x=-y\) hoặc \(y=-z\) hoặc \(z=-x\).
-Đến đây thôi bạn, câu hỏi sai rồi ạ.
\(a,\left\{{}\begin{matrix}\left|x-3y\right|\ge0\\\left|y+4\right|\ge0\end{matrix}\right.\Rightarrow VT\ge0\)
Dấu \("="\Leftrightarrow\left\{{}\begin{matrix}x-3y=0\\y+4=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=3y=-12\\y=-4\end{matrix}\right.\)
\(b,Sửa:\left|x-y-5\right|+\left(y+3\right)^2=0\\ \left\{{}\begin{matrix}\left|x-y-5\right|\ge0\\\left(y+3\right)^2\ge0\end{matrix}\right.\Rightarrow VT\ge0\)
Dấu \("="\Leftrightarrow\left\{{}\begin{matrix}x-y-5=0\\y+3=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=y+5=2\\y=-3\end{matrix}\right.\)
\(c,\left\{{}\begin{matrix}\left|x+y-1\right|\ge0\\\left(y-2\right)^4\ge0\end{matrix}\right.\Rightarrow VT\ge0\)
Dấu \("="\Leftrightarrow\left\{{}\begin{matrix}x+y-1=0\\y-2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1-y=-1\\y=2\end{matrix}\right.\)
\(d,\left\{{}\begin{matrix}\left|x+3y-1\right|\ge0\\3\left|y+2\right|\ge0\end{matrix}\right.\Rightarrow VT\ge0\)
Dấu \("="\Leftrightarrow\left\{{}\begin{matrix}x+3y-1=0\\y+2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1-3y=7\\y=-2\end{matrix}\right.\)
\(e,Sửa:\left|2021-x\right|+\left|2y-2022\right|=0\\ \left\{{}\begin{matrix}\left|2021-x\right|\ge0\\\left|2y-2022\right|\ge0\end{matrix}\right.\Rightarrow VT\ge0\)
Dấu \("="\Leftrightarrow\left\{{}\begin{matrix}2021-x=0\\2y-2022=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2021\\y=1011\end{matrix}\right.\)
Ta thấy : \(\left|x-2021\right|\ge0\forall x,\left|y-2022\right|\ge0\forall y\\ =>\left|x-2021\right|+\left|y-2022\right|\ge0\)
Mà theo đề : \(\left|x-2021\right|+\left|y-2022\right|\le0\)
=> \(\left\{{}\begin{matrix}x-2021=0\\y-2022=0\end{matrix}\right.=>\left(x;y\right)=\left(2021;2022\right)\)
\(\left|x-2\right|+\left|y-1\right|+\left(x+y-z-2\right)^{2022}=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x-2=0\\y-1=0\\x+y-z-2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=1\\z=1\end{matrix}\right.\)
\(A=5\cdot2^2\cdot1^{2020}\cdot1^{2021}=20\)
<=> x-2021=0 và y+2022=0
=>x=2021 và y=-2022
Vì \(\left(x-2021\right)^2\ge0,\left(y+2022\right)^2\ge0\)
\(\Rightarrow\left(x-2021\right)^2+\left(y+2022\right)^2\ge0\)
Dấu "=" xảy ra \(\Leftrightarrow\left\{{}\begin{matrix}x-2021=0\\y+2022=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2021\\y=-2022\end{matrix}\right.\)
Vậy \(\left(x,y\right)=\left(2021,-2022\right)\)