设z=x+yi |z-1|=1 (x-1)²+y²=1 设x-1=cosa ,y=sina |z-i| =√[x²+(y-1)²] =√[(cosa+1)²+(sina-1)²] =√(cos²a+2cosa+1+sin²a-2sina+1) =√[3+2(cosa-sina)] =√[3+2√2(cos(a+π/4)] 所以|z-i|的最小值=√(3-2√2)=√2-1 最大值=√(3+2√2)=√2+1