A.x=1,y=-1                             B.x=1,y=1

C.x=-1,y=-1                            D.x=-1,y=1

A.1+i               B.-1+i         C.1-i                 D.-1-i

A.第一象限              B.第二象限        C.第三象限              D.第四象限

A.i                                B.-i

C.-i                                 D.--i

A.1                      B.            C.                  D.

①满足z=的复数只有±1,±i  ②若a、b∈R且a=b,则(a-b)+(a+b)i是纯虚数  ③复数z∈R的充要条件是z=

A.0个                    B.1个            C.2个                  D.3个

(1)求|z|的值及z的实部的取值范围；

(2)设u=,求证:u为纯虚数；

(3)求ω-u²的最小值.