`D=2x-2-3x^2`

`=-3(x^2 - 2/3 x  + 2/3)`

`=-3(x^2 -2. x 1/3 + 1/9 - 1/9 +2/3)`

`=-3[(x- 1/3)^2 +5/9]`

`=-3(x- 1/3)^2 - 5/3`

Vì `-3(x- 1/3)^2 <= 0 AA x `

`=>-3(x- 1/3)^2  - 5/3 <= -5/3 AA x`

`-> D <= -5/3`

Dấu "=' xảy ra khi: `x- 1/3=0 <=> x=1/3`

Vậy `D_(max)=-5/3` khi `x=1/3`

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`H=10x-6x^2 +5`

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

`=-6[x^2 - 2x . 5/6 + (5/6)^2 - (5/6)^2 - 5/6]`

`=-6[(x- 5/6)^2 -55/36]`

`=-6(x- 5/6)^2 + 55/6`

Vì `-6(x- 5/6)^2 <= 0 AA x`

`=>-6(x- 5/6)^2 + 55/6 <= 55/6 AA x`

`-> H <= 55/6`

Dấu "=" xảy ra khi: `x- 5/6=0 <=> x=5/6`

Vậy `H_(max)= 55/6` khi `x=5/6`