Giải thích các bước giải:
`B=x-4x^2`
`=-4x^2+x`
`=-[4x^2-x]`
`=-[4(x^2-1/4 x)]`
`=-[4(x^2 - 2 . 1/8 x +1/64 - 1/64)]`
`=-[4(x-1/8)^2-1/16]`
`=-4(x-1/8)^2+1/16`
Do `-4(x-1/8)^2<=0∀x`
`↔️-4(x-1/8)^2+1/16<=1/16∀x`
Dấu = xảy ra khi :
`x-1/8=0↔️x=1/8`
Vậy `\text{Max}_\text{B}=1/16↔️x=1/8`
$\\$
`C=-3x(x+3)-7`
`=-3x^2-9x-7`
`=-[3x^2+9x+7]`
`=-[3(x^2+3x+7/3)]`
`=-[3(x^2+2 . 3/2 x +9/4+1/12)]`
`=-[3(x+3/2)^2+1/4]`
`=-3(x+3/2)^2-1/4`
Do `-3(x+3/2)^2<=0∀x`
`↔️-3(x+3/2)^2-1/4<=-1/4∀x`
Dấu = xảy ra khi :
`x+3/2=0↔️x=-3/2`
Vậy `\text{Max}_\text{C}=-1/4↔️x=-3/2`
