设此动点坐标为(x,y)则有:
√[x^2+(y-4)^2]=|y-3| -1
x^2+y^2-8y+16=y^2-6y+9-2|y-3|+1
x^2+6-2y+2|y-3|=0
当y≥3时有:x^2=0
当y