A.2+i              B.2-i                C.-2+i              D.-2-i

(1)若z为实数,则m=_________________;

(2)若z为纯虚数,则m=_________________.

A.C=R∪I           B.R∩I=｛0｝             C.R=C∩I            D.R∩I=

CA=CB=CD=BD=2,AB=AD=.

(1)求证:AO⊥平面BCD;

(2)求异面直线AB与CD所成角的大小;

(3)求点E到平面ACD的距离.

(1)求证:{a_n}是等比数列;

(2)若数列{a_n}的公比q=f(m),数列{b_n}满足b₁=a₁,b_n=f(b_n-1)(n∈N,n≥2),求证:{}为等差数列.

求证:对定义域内任意x都有f(x)＞0.

(1)求证:AC⊥BC₁;

(2)求证:AC₁∥平面CDB₁;

(3)求异面直线AC₁与B₁C所成角的余弦值.