— I'm waiting for my friend. If he_______, I________ swimming alone.
A:doesn't come; will go
B:won't come, will go
C:will come, won't go
D:don't come, will go
等差数列{an}中,a2+a8=4,则它的前9项和S9=( )
下列作物中,不是明朝引进的是( )
(Ⅰ)求sin A的值;
(Ⅱ)若a=4 2 ,b=5,求向量 BA→ 在 BC→ 方向上的投影.
设U=R,若集合A=x|y=logx-x2+x,则CUA等于( )