2) `B = -x^2 - 4x - 7`
`= - (x^2 + 4x+7)`
`= - (x^2 + 2.x. 2 + 2^2 ) -3`
`= -(x + 2)^2 -3 `
4) `D = -x^2 -x - 1`
`= - (x^2 + 2.x.1/2 + 1/4 + 3/4)`
`= -(x^2 + 1/2)^2 - 3/4`
6) `F = -3x^2 - 6x - 4`
`= - ((\sqrt3 x)^2 + 2. \sqrt3 x . \sqrt3 + 3 +1)`
`= -(\sqrt3 x + \sqrt3)^2 - 1`
8) `H = -4x^2 -6x - 4`
`= -(4x^2 + 2.2x. 3/2 + 9/4 + 7/4)`
`= -(2x + 3/2)^2 - 7/4`
10) `L = -1/3 x^2 + 2x -5`
`= - (1/3 x^2 + 2. 1/(\sqrt3) x . \sqrt3 + 3 + 2)`
`= -(1/3 x + \sqrt3 )^2 -2`
