`A = (9xy^2 - 6x^2y) : (-3xy) + (6x^2y + 2x^4) : 2x^2`
`= [ - (9xy^2 : 3xy) + (6x^2y : 3xy)] + (6x^2y : 2x^2 + 2x^4 : 2x^2)`
` = (-3y + 2x) + (3y + x^2)`
`= -3y + 2x + 3y + x^2`
` = x^2 + 2x`
` = (x^2 + 2x + 1) - 1`
` = (x + 1)^2 - 1`
`\forall x` ta có :
`(x+1)^2 \ge 0`
`=> (x+1)^2 - 1 \ge -1`
`=> A \ge -1`
Dấu `=` xảy ra `<=> x+1 =0 <=>x=-1`
Vậy `\text{Min}_A = -1 <=> x = -1`