【简答题】下面一组图形为三棱锥 P - ABC 的底面与三个侧面.已知 AB ⊥ BC , PA ⊥ AB , PA ⊥ AC . (1)在三棱锥 P - ABC 中,求证:平面 ABC ⊥平面 PAB ; (2)在三棱锥 P - ABC 中, M 是 PA 的中点,且 PA = BC =3, AB =4,求三棱锥 P - MBC 的体积.
【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.
【判断题】临习小篆的时候,对于有字框的笔画,一般应写出框内的笔画,随后再写外框的部分。
【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)
【单选题】I think English is too difficult. At times I feel like ______.
【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.