设Z=a+bi 则a+bi/(a-1)+bi =(a+bi)[(a-1)-bi]/(a-1)^2+b^2 =a^2-a+b^2-(2a-1)bi/(a-1)^2+b^2
为纯虚数,实部为零,虚部不为零,则 a^2-a+b^2=0 且 2a-1不等于0,b不等于0
a不等于0.5,b不等于0 (a-1/2)^2+b^2=0 为圆,将那几点扣去就行.