`#tnvt`
`B=x^2+x`
`=x^2+2.x. 1/2+1/4-1/4`
`=(x+1/2)^2-1/4`
Với mọi `x\inRR,` ta có: `(x+1/2)^2>=0`
`<=>(x+1/2)^2-1/4>=-1/4`
Dấu `=` xảy ra khi `x+1/2=0<=>x=-1/2`
Vậy `GTNNNN=-1/4` khi `x=-1/2`
`D=-x^2-x+2`
`=-x^2-2.x. 1/2-1/4+9/4`
`=-(x^2+2.x. 1/2+1/4)+9/4`
`=-(x+1/2)^2+9/4`
Với mọi `x\inRR,` ta có: `(x+1/2)^2>=0`
`=>-(x+1/2)^2<=0`
`<=>-(x+1/2)^2+9/4<=9/4`
Dấu `=` xảy ra khi `x+1/2=0<=>x=-1/2`
Vậy `GTLNN=9/4` khi `x=-1/2`
