MN ơi cứu em với

Lời giải:
$x^2-2xy+6y^2-12x+2y+41=0$

$\Leftrightarrow (x^2-2xy+y^2)+5y^2-12x+2y+41=0$

$\Leftrightarrow (x-y)^2-12(x-y)+36+5y^2-10y+5=0$

$\Leftrightarrow (x-y-6)^2+5(y-1)^2=0$

Vì $(x-y-6)^2\geq 0; (y-1)^2\geq 0$ với mọi $x,y$

Do đó để tổng trên bằng $0$ thì bản thân mỗi số trên bằng $0$

$\Rightarrow x-y-6=y-1=0$

$\Rightarrow y=1; x=7$

$\Rightarrow P=2021(10-7-2)^{2021}-8(6-7)^{2022}$

$=2021-8=2013$

\(f\left(x,y\right)=\left(x^2+4y^2-4xy\right)+\left(2x-4y\right)+1+\left(y^2-2y+1\right)+1\)

\(f\left(x,y\right)=\left(x-2y\right)^2+2\left(x-2y\right)+1+\left(y-1\right)^2+1\)

\(f\left(x,y\right)=\left(x-2y+1\right)^2+\left(y-1\right)^2+1\)

\(\left\{{}\begin{matrix}\left(x-2y+1\right)^2\ge0\\\left(y-1\right)^2\ge0\end{matrix}\right.\)=> f(x;y) >=1 >0 => dpcm

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\(f\left(x,y\right)=x^2+4y^2+1-4xy+2x-4y+y^2-2y+1+1\)

\(=\left(x-2y+1\right)^2+\left(y-1\right)^2+1\ge1>0\)

\(\Rightarrowđpcm\)

\(x^2+5y^2-4xy-6y+9=0\)

\(\Leftrightarrow\left(x^2-4xy+4y^2\right)+\left(y^2-6y+9\right)=0\)

\(\Leftrightarrow\left(x-2y\right)^2+\left(y-3\right)^2=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}x-2y=0\\y-3=0\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x=6\\y=3\end{matrix}\right.\)

\(\Rightarrow A=...\)

Ta có:

\(x^2+5y^2-4x-4xy+6y+5=0\\\Rightarrow[(x^2-4xy+4y^2)-(4x-8y)+4]+(y^2-2y+1)=0\\\Rightarrow[(x-2y)^2-4(x-2y)+4]+(y-1)^2=0\\\Rightarrow(x-2y-2)^2+(y-1)^2=0\)

Ta thấy: \(\left\{{}\begin{matrix}\left(x-2y-2\right)^2\ge0\forall x,y\\\left(y-1\right)^2\ge0\forall y\end{matrix}\right.\)

\(\Rightarrow\left(x-2y-2\right)^2+\left(y-1\right)^2\ge0\forall x,y\)

Mà: \(\left(x-2y-2\right)^2+\left(y-1\right)^2=0\)

nên: \(\left\{{}\begin{matrix}x-2y-2=0\\y-1=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=2y+2\\y=1\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x=2\cdot1+2=4\\y=1\end{matrix}\right.\)

Thay \(x=4;y=1\) vào \(P\), ta được:

\(P=\left(4-3\right)^{2023}+\left(1-2\right)^{2023}+\left(4+1-5\right)^{2023}\)

\(=1^{2023}+\left(-1\right)^{2023}+0^{2023}\)

\(=1-1=0\)

Vậy \(P=0\) khi \(x=4;y=1\).

Câu 2 

1, a, \(x^2+9xy+8y^2-8y-x=x^2+xy+8xy+8y^2-\left(8y+x\right)\)

\(=\left(x+y\right)\left(8y+x\right)-\left(8y+x\right)=\left(8y+x\right)\left(x+y-1\right)\)

b, \(x^3+5x-6=x^3-x^2+x^2-x+6x-6\)

\(=x^2\left(x-1\right)+x\left(x-1\right)+6\left(x-1\right)=\left(x-1\right)\left(x^2+x+6\right)\)

Câu 2:

b) \(x^3+5x-6=x^3+x^2+6x-x^2-x-6\)         \(=x\left(x^2+x+6\right)-\left(x^2+x+6\right)\) \(=\left(x-1\right)\left(x^2+x+6\right)\) 

Câu 1 giữa 2 phân thức đầu tiên là dấu gì hả em?