Đáp án:
`D_(max)=209/16` khi `x=-7/8`
Giải thích các bước giải:
`D=-4x²-7x+10`
`=-4(x²+7/4x-5/2)`
`=-4(x²+7/4x+49/64-209/64)`
`=-4(x²+7/4x+49/64)+209/16`
`=-4[x²+2.x. 7/8+(7/8)^2]+209/16`
`=-4(x+7/8)^2+209/16`
Ta có:`(x+7/8)^2>=0AAx`
`⇒4(x+7/8)^2>=0AAx`
`⇒-4(x+7/8)^2<=0AAx`
`⇒-4(x+7/8)^2+209/16<=209/16AAx`
Vậy `D_(max)=209/16` khi `x+7/8=0⇔x=-7/8`
