`@` `color[#480209][d]``color[#81020E][t]``color[#A80111][t]`

Đáp án:

`A=(3x^2-4x+5)/(2x^2+6)`

`A=(3(x^2+3)-4x-4)/(2(x^2+3))`

`A=3/2-(2x+2)/(x^2+3)`

`A=1/2-(2x+2-x^2-3)/(x^2+3)`

`A=1/2-(-x^2+2x-1)/(x^2+3)`

`A=1/2+((x-1)^2)/(x^2+3)`

T/c:

`(x-1)^2 ge 0 AA x;x^2+3 ge 3 AA x`

`to ((x-1)^2)/(x^2+3) ge 0/3=0 AA x`

`to A=1/2+((x-1)^2)/(x^2+3) ge 1/2+0=1/2 AA x`

`-` DBXR khi :

`(x-1)^2=0 to x-1=0 to x=1`

Vậy `A_(min)=1/2⇔x=1`