Đáp án:
`↓↓`
Giải thích các bước giải:
`a) | x - 8 | + | y + 2 |`
Ta có: `| x - 8 | >= 0 ∀x`
`| y + 2 | >= 0 ∀y`
`=> | x - 8 | + | y + 2 | >=0 ∀x,y`
Dấu "=" xảy ra `<=>` $\left\{\begin{matrix}|x-8| = 0& \\|y+2| = 0& \end{matrix}\right.$
⇒ $\left\{\begin{matrix}x-8 = 0& \\y+2 = 0& \end{matrix}\right.$
⇒ $\left\{\begin{matrix}x=8 & \\y=-2 & \end{matrix}\right.$
`b) xy = x+y`
`=> xy - x - y = 0 `
`=> x ( y - 1 ) -1 ( y - 1 ) - 1 = 0`
`=> ( x - 1 ) ( y - 1 ) = 1`
Ta có bảng:
$\begin{array}{|c|c|}\hline x-1&1&-1\\\hline y-1&1&-1\\\hline x&2&0 \\\hline y&2&0\\\hline \end{array}$
`c) xy = x - y`
`=> xy - x + y = 0`
`=> x ( y - 1 ) + 1 ( y - 1 ) + 1 = 0`
`=> ( x + 1 ) ( y - 1 ) = -1`
Ta có bảng:
$\begin{array}{|c|c|}\hline x+1&1&-1\\\hline y-1&-1&1\\\hline x&0&-2 \\\hline y&0&2\\\hline\end{array}$
