`(x-5)^2≥0`
`| 3y-6|≥0`
`a=(x-5)^2 + | 3y-6| -3≥-3`
`''=''` xẩy ra khi :
⇔\(\left[ \begin{array}{l}(x-5)^2=0\\| 3y-6|=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=5\\y=2\end{array} \right.\)
vậy `min a = -3` khi \(\left[ \begin{array}{l}x=5\\y=2\end{array} \right.\)