`text{ta có}`
`Q=-2x^2+8x-22`
`=-2(x^2-4x+4) - 14`
`=-2(x-2)^2-14`
`text{vì} (-2)^2 >=0 AA x => -2(x-2)^2 <=0 AA x`
`=> -2(x-2)^2 -14 <=-14 AA x`
`=>Q<=-14 AA x `
`text{dấu = xảy ra khi} x-2=0 => x=2`
`text{Vậy} Q_(Max) = -14 khi x=2`
~~~~~~~GOOD LUCK~~~~~~~~
