The teacher asked the students to stop talking and ____ (listen) to her.
有一焦距为10cm的凸透镜,将物体从离凸透镜30cm处沿主光轴移到距透镜20cm处,这个过程中所成的像()
若x,y为实数,且满足|x﹣3|+y+3=0,则(xy)2015的值是( )
点A在点O的南偏东30°,点B在点O的北偏西70°,则OA,OB这两条射线构成的角等于( )