如图,已知A1B1C1﹣ABC是正三棱柱,D是AC中点.
(1)证明AB1∥平面DBC1;
(2)假设AB1⊥BC1,BC=2,求线段AB1在侧面B1BCC1上的射影长.
(1)证明:∵A1B1C1﹣ABC是正三棱柱,
∴四边形B1BCC1是矩形.连接B1C,交BC1于E,则B1E=EC.连接DE.
在△AB1C中,∵AD=DC,∴DE∥AB1,又AB1⊄平面DBC1.DE⊂平面DBC
小红要过生日了,为了筹备生日聚会,准备自己动手用纸板制作一个底面半径为9cm,母线长为30cm的圆锥形生日礼帽,则这个圆锥形礼帽的侧面积为( )
Hunan TV station is very popular among young people in China. Are you interested in it? Do you think it's good or bad? Some students had a discussion about this question. Here are some opinions.
Good
Nancy
I know a lot of great people who are introduced by Hunan TV station. They are good at singing, dancing and acting because they always spend plenty of time practicing these things. They should be our heroes.
Tommy
Every weekend I watch its different kinds of programs with my parents. And it helps my parents know about me and my favorite things. Besides, it's also a good way to relax after a week's schoolwork.
Bad
Lily
I don't like the program Supper Girl. It attracts too much of our attention. Many of us always talk about who is beautiful or who will win. Sometimes we even talk about it in class and forget our study. It's not a good thing for students.
Daniel
I don't think Hunan TV station is useful. Some hosts of some programs just try to play jokes on others or themselves. It's a waste of time. We can't learn anything from them. We should make a rule to keep students away from these boring programs.
为筹备学校2013年元旦晚会,准备工作中班长对全班学生爱吃哪几种水果作了调查。那么最终买什么水果,下面的调查数据中最值得关注的( )。