a) `B=x^2-x+1`
`=x^2-2. 1/2x+1/4+3/4`
`=(x-1/2)^2+3/4ge3/4`
b) `C=2x^2-2x+4`
`=2(x^2-x+2)`
`=2(x^2-2. 1/2x+1/4)+7/2`
`=2(x-1/2)^2+7/2ge7/2`
c) `D=-3x^2-3x+6`
`=-3(x^2+x-2)`
`=-3(x^2+2. 1/2x+1/4-9/4)`
`=-3(x+1/2)^2+27/4le27/4`
d) `E=-2x^2+x`
`=-2(x^2-2. 1/4x+1/16)+1/8`
`=-2(x-1/4)^2+1/8le1/8`