|m+2|+(n-4)平方=0
m+2=0
m=-2
(n-4)^2=0
n=4
(x平方＋y平方)－(mxy＋n)
=(X^2+y^2)-(-2XY+4)
=X^2+y^2+2XY-4
=(X+Y)^2-4
=(X+Y-2)(X+y+2)
不懂的欢迎追问,