a,`x^2 + x +1 = (x^2 + x + 1/4) + 3/4 = (x+1/2)^2 +3/4`
`text{vì } (x+1/2)^2 >=0 AA x `
`=> (x+1/2)^2 + 3/4 >0 AA x (text{đpcm})`
b,`-x^2 + 2x - 2022 = -(x^2 - 2x + 1) - 2021 = -(x-1)^2-2021`
`text{vì } (x-1)^2 >=0 AA x => -(x-1)^2 <=0 AA x`
`=> -(x-1)^2 - 2021 < 0 AA x => (text{đpcm})`