如图,AB为⊙O的切线,AC、BD分别与⊙O切于C、D点,若AB=5,AC=3,则BD的长是____
下列属于种群的是()
已知|AB|=2,动点P满足|PA|=2|PB|,试建立恰当的直角坐标系,动点P的轨迹方程为____.
Tourists were feasting their eyes on the ocean scenery and suddenly they spotted an Iceberg (冰山)f____at a distance.