如图，在几何体SABCD中，AD⊥平面SCD，BC⊥ 平面SCD，AD=DC=2，BC=1，又SD=2，∠SDC=120°. （1）求SC与平面SAB所成角的正弦值； （2）求平面SAD与平面SAB所成的锐
从甲、乙，……，等人中选出名代表，那么（1）甲一定当选，共有 种选法．（2）甲一定不入选，共有 种选法.（3）甲、乙二人
人在距地面高h、离靶面距离L处，将质量m的飞镖以速度v0水平投出，落在靶心正下方，如图6所示。只改变h、L、v0四个量中的一个，可使飞镖投中靶心的
--- Would you mind speaking a little slowly? I ___ quite catch you? --- _____. A. can’t; Of course B. didn’t; Not at all. C. didn’t; You’d better no
边长为10cm的正方体铁块，置于水平地面上，用一弹簧秤钩住铁块向上用力拉，铁块仍在地面上静止，若此时地面承受的压强是7044Pa，弹簧秤的读数是多
--- Would you please tell me something about your travel in Sydney? --- ________ A. Excuse me. I’m afraid not. B. It’s very nice of you to say so C. Certainly. I’ll be glad to
根据句意及汉语提示完成单词 1． Teachers are usually ________(严格的) with their students in class. 2．Whatever she does, I will ________ (支持) her. 3．His sister ________ (进
已知棱长为a的正四面体P—ABC与Q—A1B1C1,使面ABC与面A1B1C1重合得一个多面体,则这个多面体( ) A.是正六面体
