`C = 4x^2 + 8x + 10`
`C = 4x^2 + 2 . 2x . 2 + 4 + 6`
`C = (2x + 2)^2 + 6 ≥ 6`
`text(Min)` `text(C = 6 khi x = -1)`
`D = 1/4x^2 - 4x + 6`
`D = 1/4x^2 - 2 . 1/2x . 4 + 16 - 10`
`D = (1/2x - 4)^2 - 10 ≥ -10`
`text(Min)` `text(D = -10 khi x = 8)`
`E = 9x^2 - 6x + 4`
`E = 9x^2 - 2 . 3x . 1 + 1 + 3`
`E = (3x - 1)^2 + 3 ≥ 3`
`text(Min)` `text(E = 3 khi x =)` `1/3`