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b) Có x+y+z=0 => \(\left\{{}\begin{matrix}x+y=-z\\y+z=-x\\x+z=-y\end{matrix}\right.\)
=> B = \(-xyz\) = -2
a) Có x + y + 1 =0 => x + y = -1
\(x^2\left(x+y\right)-y^2\left(x+y\right)+x^2-y^2+2\left(x+y\right)+3\)
= \(\left(x+y\right)\left(x^2-y^2\right)+\left(x-y\right)\left(x+y\right)+2\left(x+y\right)+3\)
= \(\left(x+y\right)^2\left(x-y\right)+\left(x-y\right)\left(x+y\right)+2\left(x+y\right)+3\)
Thay x + y = -1, ta có:
A = x - y - x + y - 2 + 3
= 1
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{3}=>\left\{{}\begin{matrix}x=\dfrac{5y}{7}\\z=\dfrac{3y}{7}\end{matrix}\right.\) thay x,z vào \(x^2+y^2-z^2=585\)
\(=>\left(\dfrac{5y}{7}\right)^2+y^2-\left(\dfrac{3y}{7}\right)^2=585=>y=\pm21\)
\(=>\left\{{}\begin{matrix}x=\dfrac{5.(\pm21)}{7}=\pm15\\z=\dfrac{3\left(\pm21\right)}{7}=\pm9\end{matrix}\right.\)
vậy (x,y,z)\(\in\left\{\left(15;21;9\right)\left(-15;-21;-9\right)\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(x+\frac{2}{3}\right)^{2012}+\left|y-\frac{1}{4}\right|^{2000}+\left(x-y-z\right)^{2014}=0\)
\(\Leftrightarrow\hept{\begin{cases}x+\frac{2}{3}=0\\y-\frac{1}{4}=0\\x-y-z=0\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}x=-\frac{2}{3}\\y=\frac{1}{4}\\z=-\frac{11}{12}\end{cases}}\).
![](https://rs.olm.vn/images/avt/0.png?1311)