—______! The man next to me has just gone. The seat is empty now.
A:You'd better not.
B:Of course not
C:Take care
D:Wait a minute
在极坐标系中,直线 ρcos(θ+π3)=1 与曲线 ρ=r ( r>0 )相切,求 r 的值.
如图,直角坐标系中,点A(-2,2)、B(0,1)点P在x轴上,且△PAB是等腰三角形,则满足条件的点P共有( )个