计算 (11 21:57:25) X2+Y2-4X+Y+4.5=0,求Y-X+3XY的值

计算 (11 21:57:25) X2+Y2-4X+Y+4.5=0,求Y-X+3XY的值
计算 (11 21:57:25)
 
X2+Y2-4X+Y+4.5=0,求Y-X+3XY的值

计算 (11 21:57:25) X2+Y2-4X+Y+4.5=0,求Y-X+3XY的值
题目对吗?
是不是x^2+y^2-4x+y+4.25=0
x^2+y^2-4x+y+4.25=0
(x-2)^2+(y+0.5)^2=0
所以x=2,y=-0.5
所以：
y-x+3xy
=-0.5-2+3*2*(-0.5)
=-2.5-3
=-5.5

提取公因式

X^2+Y^2-4X+Y+4.25=0
x^2-4x+4+y^2+y+1/4=0
(x-2)^2+(y+1/2)^2=0
x=2
y=-1/2
y-x+3xy
=-1/2-2+3*(-1/2)*2
=-11/2

x2-4x+4+y2+y+1/2=0
(x-2)2+(y+1/2)2=0
因为0+0=0
所以 x=2 y=-1/2
将其代入
y-x+3xy=-1/2-2-3=-11/2