Đáp án: `a, x = 5/2 ; y = 7/2`
`b, x = 4 ; y = 2/9`
Giải thích các bước giải:
`a,` Ta có: `|2x - 5| + |x - y + 1| = 0`
Mà $\left\{ \begin{array}{l}|2x - 5| ≥ 0\\|x - y + 1| ≥ 0\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}|2x - 5| = 0\\|x - y + 1| = 0\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}2x - 5 = 0\\x - y + 1 = 0\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}2x = 5\\x - y = -1\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}x = \frac{5}{2}\\\frac{5}{2} - y = -1\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}x = \frac{5}{2}\\y = \frac{5}{2} + 1 = \frac{5}{2} + \frac{2}{2} = \frac{7}{2} \end{array} \right.$
Vậy `x = 5/2 ; y = 7/2`
`b,` Ta có: `|3x - 12| + |9y - 2|^2020 = 0`
Mà $\left\{ \begin{array}{l}|3x - 12| ≥ 0\\|9y - 2|^{2020} ≥ 0\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}|3x - 12| = 0\\|9y - 2|^{2020} = 0\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}3x - 12 = 0\\9y - 2 = 0\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}3x = 12\\9y = 2\end{array} \right.$
`⇒` $\left\{ \begin{array}{l}x = 4\\y = \frac{2}{9}\end{array} \right.$
Vậy `x = 4 ; y = 2/9`
