题目

如图，在四棱锥P—ABCD中，底面ABCD是正方形，侧棱PD⊥底面ABCD，PD=DC,E是PC的中点，作EF⊥PB交PB于点F.  (1)求证：PA∥平面EDB；(2)求证：PB⊥平面EFD；(3)求二面角C-PB-D的大小. 答案：思路解析：本题涉及的问题包括：判定直线与平面平行和垂直，计算二面角的大小.这些问题都可以利用向量方法解决.由于已知条件中四棱锥的底面是正方形，一条侧棱垂直于底面，所以非常适合建立空间直角坐标系表示向量. 解：如题图，建立空间直角坐标系，点D为坐标原点，设DC=1.(1)证明：连结AC交BWith long brown hair, deep blue eyes, a tall and thin figure(身躯) Brad Pitt seems to be a born actor.He made his first appearance in a film in 1990.Though he was in the film for only 14 minutes, people flooded the cinema to see him.In his next film Pitt played the role of a fisherman.To make the film better, he learned the skill of fishing from a fisherman. Pitt, caring more about roles than money, has a special favor for the “hard” roles.After reading the screenplay(剧本) of “Legends of the Fall”, he was attracted by the leading character.He asked for a lower pay from the shooting team and was willing to work in hard conditions in the Rocky Mountains for six months.“The film gives the chance to know life.I shall always remember the time when we were making the film,” Pitt said after completing it fully. Pitt started his dream of art when he was in university.Though born in a common family in 1964, he showed his interest in film at an early age.After leaving high school, he went to university to study law.Because he loved film more than law, shortly before he could graduate, he dropped out for a life of his own, with only 325 dollars in hand, sometimes as a porter or a waiter.Thanks to his hard work, he finally opened up a new field of his own. 1.Pitt acted his first film at the age of        . A．6                B．14               C．26               D．36 2.The underlined expression “a born actor” means        . A．he was born in an actor family B．he became an actor soon after he was born C．he was an actor when he was born D．he has a strong natural ability to be an actor 3.From the passage we know        . A．Pitt became known as an actor at an early age. B．To achieve his goal, Pitt suffered a lot before success C．it was wrong of Pitt not to finish his university education D．In order to develop his interest, Pitt failed to enter university 4.Which of the following words can best describe the character of Pitt? A．Devoted.          B．Generous.         C．Selfish.           D．Mean.