(X^2+1)(Y^2+1)=4XYx^2y^2+(x^2+y^2)+1-4xy=0(x^2y^2-2xy+1)+(x^2-2xy+y^2)=0(xy-1)^2+(x-y)^2=0平方数非负要使等式成立 只能xy-1=0x-y=0x=1,y=1 或者x=-1,y=-1 X^2-3Y+2=1-3+2=0或者X^2-3Y+2=1+3+2=6
