P是△ABC所在平面外一点,若△ABC与△PBC都是边长为2的正三角形,PA=,那

P是△ABC所在平面外一点,若△ABC与△PBC都是边长为2的正三角形,PA=

,那么,二面角P-BCA的大小是___________________________.

答案

解析：取BC的中点D,连结PD、AD,

∵△ABC、△PBC均为正三角形,

∴PD⊥BC,AD⊥BC.

∴∠PDA为二面角PBCA的平面角.

又PD=AD=,PA=,

∴∠PDA=90°.

答案：90°

相关题目

命题作文题目：细微之处见真情文体不限（诗歌除外），600

命题作文题目：细微之处见真情文体不限（诗歌除外），600～800字，文中不出现真实的人名、地名和校名。

经检测，刚挤出的鲜牛奶中有两种分子，分子式分别为：C12H2

经检测，刚挤出的鲜牛奶中有两种分子，分子式分别为：C12H22O11和C1864H3012N168O221的化学物质，这两种物质分别是（） A．脂肪和核酸 �

Joe, 75, lived very happily and had a beautiful family. He had four grandchildr

Joe, 75, lived very happily and had a beautiful family. He had four grandchildren, and they all visited him during their holidays. Before they came to visit, Joe got his home ready for the childre

把由NaOH、AlCl3、MgCl2三种固体组成的混合物溶于足量水中，有

把由NaOH、AlCl3、MgCl2三种固体组成的混合物溶于足量水中，有0.58g白色沉淀生成，向所得滤液(滤出0.58g沉淀),逐滴加入0.5mol/L的盐酸，加入盐酸的体积和生

He’s got himself into a dangerous situation _____ he is likely to lose control

He’s got himself into a dangerous situation _____ he is likely to lose control over the plane. A. where B. which C. while D. why

【物理选修3-5】（15分）（1）(5分)如图所示为氢原子的能

【物理选修3-5】（15分）（1）(5分)如图所示为氢原子的能级示意图，一群氢原子处于n=3的激发态，在向较低能级跃迁的过程中向外发出光子，用这些

2014年中央电视台“3.15”晚会上，曝光了麦当劳、家乐福等知

2014年中央电视台“3.15”晚会上，曝光了麦当劳、家乐福等知名企业的个别门店随意修改食品保质期等违法行为。食品安全再度敲响警钟。这再一次警示

Still seeking a destination for your weekend break? There are some places which

Still seeking a destination for your weekend break? There are some places which are probably a mere wall away from your college. King’s Art Centre A day at the Centre could mean a visit to

P是△ABC所在平面外一点,若△ABC与△PBC都是边长为2的正三角形,PA=,那

答案

相关题目

最新题目