二次函数y=3x2的图象如图,点O为坐标原点,点A在y轴的正半轴上,点B、C在二次函数y=3x2的图象上,四边形OBAC为菱形,且∠OBA=120°,则菱形OBAC的面积为____ .
Before entering the room,I was asked to show the soldier the________ of my suitcase.
板书是浓缩的教学案。见如图板书设计,其标题应为( )