\(\left(x^4-2x^2+1\right)+\left(y^4-2y^2+1\right)+\left(z^4-2z^2+1\right)=0\)

\(\Leftrightarrow\)\(\left(x^2-1\right)^2+\left(y^2-1\right)^2+\left(z^2-1\right)^2=0\)

\(\Leftrightarrow\)\(\hept{\begin{cases}\left(x-1\right)\left(x+1\right)=0\\\left(y-1\right)\left(y+1\right)=0\\\left(z-1\right)\left(z+1\right)=0\end{cases}}\)\(\Rightarrow\)\(x,y,z\in\left\{1;-1\right\}\)

Mà \(\hept{\begin{cases}x^{2022}\ge0\forall x\\y^{2020}\ge0\forall y\\z^{2018}\ge0\forall z\end{cases}}\) nên P nhận giá trị không đổi khi \(x,y,z\in\left\{1;-1\right\}\)

\(\Rightarrow\)\(P=1+1+1=3\)

Thay \(y=\frac{5}{3}x;\)\(z=2x\) vào \(\frac{t}{x}-\frac{t}{y}+\frac{t}{z}=\frac{9}{10}\), ta có:

\(t\left(\frac{1}{x}-\frac{3}{5x}+\frac{1}{2x}\right)=\frac{9}{10}\)⇒ \(\frac{9t}{10x}=\frac{9}{10}\Rightarrow t=x\)

Lần lượt thay \(y=\frac{5}{3}x;z=2x;t=x\)vào P, ta có:

\(P=\frac{x^2}{\frac{5}{3}.x^2}+\frac{x^2}{\frac{10}{3}.x^2}+\frac{x^2}{2x^2}=\frac{3}{5}+\frac{3}{10}+\frac{1}{2}=\frac{7}{5}\)

Chứng minh

căn 9 + căn 17 + căn 9 - căn 17 =căn 34

căn 8 + căn 15 + căn 8 - căn 15 =căn 30

ta có  \(7x^2-13xy-2y^2=0\)

  \(7x^2-14xy+xy-2y^2=0\)

7x(x-2y)+y(x-2y)=0

(7x+y)(x-2y)=0

=>. 7x+y=0   hoặc   x-2y=0

=>   y=-7x     hoặc x=2y

Thay lần lượt vào A là OK nha bn !

\(\frac{1}{x}+\frac{1}{y}+\frac{1}{z}=\frac{1}{x+y+z}\)

\(\Leftrightarrow\frac{1}{x}+\frac{1}{y}=\frac{1}{x+y+z}-\frac{1}{z}\)

\(\Leftrightarrow\frac{x+y}{xy}=\frac{z}{\left(x+y+z\right).z}-\frac{x+y+z}{z.\left(x+y+z\right)}=\frac{-x-y}{z.\left(x+y+z\right)}\)

\(\Leftrightarrow\frac{x+y}{xy}=\frac{x+y}{-z.\left(x+y+z\right)}\)

TH1: x+y=0

=> x=-y => P=0

TH2: xy=-z.(x+y+z)

\(\Leftrightarrow xy=-xz-zy-z^2\Leftrightarrow xy+xz+zy+z^2=0\Leftrightarrow x.\left(y+z\right)+z.\left(y+z\right)=0\)

\(\Leftrightarrow\left(x+z\right).\left(y+z\right)=0\Leftrightarrow\orbr{\begin{cases}x=-z\\y=-z\end{cases}\Rightarrow P=0}\)