`1,`
`a) A=4x^2+4x+11`
`A=(4x^2+4x+1)+10`
`A=(2x+1)^2+10>=10`
Dấu = xảy ra khi `2x+1=0<=>x=-1/2`
Vậy `minA=10` khi `x=-1/2`
`b) C=x^2-2x+y^2-4y+7`
`C=(x^2-2x+1)+(y^2-4y+4)+2`
`C=(x-1)^2+(y-2)^2+2>=2`
Dấu = xảy ra khi `x-1=0; y-2=0<=>x=1;y=2`
Vậy `min C=2` khi `x=1; y=2`
`2,`
`a) A=5-8x-x^2`
`A=-(x^2+8x-5)`
`A=-(x^2+8x+16-21)`
`A=21-(x+4)^2<=21`
Dấu =xảy ra khi `x+4=0<=>x=-4`
Vậy `maxA=21` khi `x=-4`
`b) B=5-x^2+2x-4y^2-4y`
`B=-(x^2-2x+4y^2+4y-5)`
`B=-[(x^2-2x+1)+(4y^2+4y+1)-7]`
`B=7-[(x-1)^2+(2y+1)^2]<=7`
Dấu = xảy ra khi `x-1=0; 2y+1=0 <=>x=1; y=-1/2`
Vậy `maxB=7` khi `x=1; y=-1/2`
