【简答题】已知三棱锥P-ABC,PA⊥AB,PA⊥AC,∠BAC=120°,PA=AB=AC=2,则三棱锥的外接球体积为________.
【单选题】up late at night is bad for our health.
【单选题】(二)阅读下面短文,回答问题
市场是物质生活的基本方式.不过,在现代之前,市场是嵌入在社会之内的,它受到社会主流价值观和生活方式的规范,并且当它试图越出这些规范时会受到社会机制的惩罚。现代社会的市场生活逐渐地克服了来自宗教和其他方面的规范力量,使市场成为占据主导的生活方式和价值观念,于是,社会被嵌入在市场之内了,卡尔·博兰尼称之为“市场社会”。在这一转型期出现的最显著的行为经济学特征,被称为“消费...
C.
跨过金钱、权力、名誉的桥,走到真实生活的彼岸
【简答题】如图,已知三棱锥P﹣ABC中,PA⊥PC,D为AB中点,M为PB的中点,且AB=2PD. (Ⅰ)求证:DM∥面PAC; (Ⅱ)找出三棱锥P﹣ABC中一组面与面垂直的位置关系,并给出证明(只需找到一组即可)
【简答题】已知三棱锥P-ABC中,PA⊥ABC,AB⊥AC,PA=AC=½AB,N为AB上一点,AB=4AN,M,S分别为PB,BC的中点. (Ⅰ)证明:CM⊥SN; (Ⅱ)求SN与平面CMN所成角的大小.
【简答题】已知三棱锥P-ABC中,PA⊥AB,PA⊥AC,∠ACB=90°(如图) (1)求证:PA⊥BC; (2)若PA=AC=BC=1,求点C到平面PAB的距离.
【简答题】B. My secret for staying young is . Put all attention to the part of you---your brain and keep it young and growing. Keep your mind awake and you’ll stay young all over. These are exciting time....
【单选题】She is a diligent student, and all her spare time she has _____ staying in the library.
【单选题】What is the sentence problem of the following sentence? Getting married is easy; staying married is a different matter.