Min 3 (x-2)+4 (6-x)

`A=3\sqrt{x-2}+4\sqrt{6-x}` `(2<=x<=6)`

`A^2=9(x-2)+16(6-x)+24\sqrt{(x-2)(6-x)}`

`=-7x+78+24\sqrt{(x-2)(6-x)}` 

`>= -7 . 6+78+0`

`=36`

`→` `A >= 6`

Dấu "=" xảy ra khi: `x=6.`