`A = x^2 - 6x + 45`
`<=> A = x^2 - 6x + 9 + 36`
`<=> A = ( x- 2 )^2 + 36`
`( x - 2)^2 ≥ 0 ; 36 > 0`
`=> A > 0`
`B = x^2 + 4x + 18`
`<=> B = x^2 + 4x + 4 + 14`
`<=> B = ( x + 2)^2 + 14`
`( x+2)^2 ≥ 0 ; 14 > 0`
`=> B > 0`
`D = x^2 + 3x + 11`
`<=> D = x^2 + 2 .x . 3/2 + 9/4 + 35/4`
`<=> D = ( x + 3/2 )^2 + 35/4`
`(x+ 3/2 )^2 ≥ 0 ; 35/4 > 0`
`=> D > 0`
`E = 4x - 4x + 5`
`<=> E = 0 + 5 = 5 > 0`
