`A=x^2+4x+25`
`=(x+2)^2+2`1≥21`
`=>` MinA = 21 `<=>x=-2`
`B=-1/4x^2+x+2018`
`=-(1/2x+1)^2+2019≤2019`
`=>` MaxB = 2019 `<=>1/2x+1=0`
`<=>1/2x=1`
`<=>x=2`
`C=x^2-2xy+2y^2+2y+17`
`=(x-y)^2+(y+1)^2+16≥16`
`=>` Min C= 16 `<=>x-y=0;y+1=0`
`<=>x=y=-1`
`D=2x^2+10xy+25y^2+4x+2019`
`=(x+2y)^2+(x+2)^2+2015≥2015`
`=>` MinD = 2015 `<=>x+2y=0;x+2=0`
`<=>2y=x=-2;x=-2`
`<=>y=-1;x=-2`