x^2-2x+y^2-4y+5=0,所以:(x-1)^2+(y-2)^2=0
所以:x-1=0,y-2=0,解得:x=1,y=2
所以:9x^2y^2-12x^3y^2+4x^4y^2=9y^2-12y^2+4y^2=y^2=4