如图,岛P位于岛Q的正西方,P、Q两岛间的距离为20(1+3)海里,由岛P、Q分别测得船R位于南偏东30°和南偏西45°方向上,则船R到岛P的距离为( )
读台湾海峡两岸地区图,完成下列各题
判断下面的图形是否是直角? ( )
The teacher walked into the classroom a smile on his face.