tim gtln ,gtnn E=x ²-11x=30 p= -3x ²-12x-25

Đáp án:

`E = x^2 - 11x + 30`

`= x^2 - 2.(11/2)x + 121/4 - 1/4`

` = ( x - 11/2)^2 - 1/4`

Ta có

` ( x - 11/2)^2 \geq 0`

` => ( x - 11/2)^2  - 1/4 \geq -1/4`

` => E_{min} = -1/4` khi ` x = 11/2`

`P = -3x^2 - 12x - 25`

` = -3.(x^2 + 4x + 4) - 13`

` = -3.(x+2)^2 - 13`

Ta có

` (x+2)^2 \geq 0`

` => -3(x+2)^2 \leq 0`

` => -3(x+2)^2 - 13 \leq -13`

` => P_{max} = -13` khi ` x =- 2`