在右图所示的多面体中,下部ABCD-A′B′C′D′为正方体,点P在DD′的延长线上,且PD′=D′D,M、N分别为△PA′B′和△PB′C′的重心.(1)已知R为棱PD上任意一点,求证:MN∥平面RAC;(2)求二面角M-BC-D的正切值大小. 扫码下载作业帮搜索答疑一搜即得 答案解析 查看更多优质解析 解答一 举报 (1)连PM并...
一,据首字母补全单词)1.Le't go to a r___2.Pople often put mony in the b___3.The head teather (校长)is in her o___4.IS there a bookshop n___ to the park.5.She p___200 yuan a week for this house.=,根据提示内容补全句子1.(park)(zoo)(bank)The zoo2.(前)(post office)...