`C=-x^2-6x-11`
`⇔C=-(x^2+6x+9)-2`
`⇔C=-(x+3)^2-2≤-2`
`''=''`xẩy ra khi :
`x+3=0`
`⇔x=-3`
vậy `maxC=-2 `khi `x=-3`
`D=-x^2-x-1`
`⇔D=-(x^2+x+1/4)-3/4`
`⇔D=-(x+1/2)^2-3/4≤-3/4`
`''=''`xẩy ra khi :
`x+1/2=0`
`⇔x=-1/2`
vậy `maxD=-3/4 `khi `x=-1/2`
`E=-x^2-3x-5`
`⇔E=-(x^2+3x+9/4)-(11)/4`
`⇔E=-(x+3/2)^2-(11)/4≤-(11)/4`
`''=''`xẩy ra khi :
`x+3/2=0`
`⇔x=-3/2`
vậy `maxE=-(11)/4 `khi `x=-3/2`
`F=-3x^2-6x-4`
`⇔F=-3(x^2+2x+1)-1`
`⇔F=-3(x+1)^2-1≤-1`
`''=''`xẩy ra khi :
`x+1=0`
`⇔x=-1`
vậy `maxE=-1 `khi `x=-1`
`G=-5x^2+7x-5`
`⇔G=-5(x^2-7/5 x+(49)/(100))-(51)/(20)`
`⇔G=-5(x-7/(10))^2-(51)/(20)≤-(51)/(20)`
`''=''`xẩy ra khi :
`x-7/(10)=0`
`⇔x=7/(10)`
vậy `maxG=-(51)/(20)` khi `x=7/(10)`
`H=-4x^2+6x-4`
`⇔H=-4(x^2-3/2 x +9/(16))-7/4`
`⇔H=-4(x-3/4)^2-7/4≤-7/4`
`''=''`xẩy ra khi :
`x-3/4=0`
`⇔x=3/4`
vậy `maxH=-7/4 ` khi `x=3/4`
