` A = 2x^2 + 3x + 15`
` = 2(x^2 + 3/(2)x) + 15`
` = 2(x^2 + 2.3/(4)x + 9/16) - 9/8 + 15`
` = 2.(x+3/4)^2 + 111/8 \geq 111/8`
` => A_{min} = 111/8` ; khi ` x = -3/4`
` D = 4 + 2x - x^2 = -(x^2 - 2x -4) = -(x^2-2x +1) -3`
` = -(x-1)^2 -3 \leq -3`
` => D_{max}= -3` khi ` x = 1`
` E = 1 + 3x - 2x^2 = -2(x^2 - 3/(2)x ) + 1`
` = -2.(x^2 -3/(2)x + 9/16) + 9/8 + 1`
` = -2(x-3/4)^2 + 17/8 \leq 17/8`
`=> E_{max} = 17/8` khi ` x = 3/4`
