Đáp án:
`x^2-2xy+2y^2-2x+6y+5=0`
`<=>x^2-2xy+y^2-2x+2y+y^2+4y+5=0`
`<=>(x-y)^2-2(x-y)+1+y^2+4y+4=0`
`<=>(x-y-1)^2+(y+2)^2=0`
Vì `(x-y-1)^2>=0,(y+2)^2>=0`
`=>(x-y-1)^2+(y+2)^2>=0`
Mà đề cho `(x-y-1)^2+(y+2)^2=0`
Dấu "=" xảy ra khi `y=-2,x=y+1=-1`
`=>P=(3x^2y-1)/(4xy)`
`P=(3.(-2).(-1)^{2}-1)/(4.(-2).(-1))`
`P=(-6-1)/(8)=-7/8`