题目

如图，在平行四边形OABC中，点A(3,0)，C(1,3)，过点C做CD⊥AB交AB于点D， 求：（1）OC所在直线的斜率；                  （2）CD所在直线的方程。 答案：解：如图，A(3,0)，C(1,3)。所以，B(4,3)         （2分） ①                                （4分） ② 因为, 所以.且CD⊥AB ,                           （8分） 所以CD所在直线的方程为：  （10分）26、Before you go to another country it is a great help if you know the language and some of the customs of the country. When people meet each other for the first time in Britain, they say, “How do you do? ”and shake hands. Usually they do not shake hands when they just meet or say goodbye. But they shake hands after they haven’t met for a long time or when they will be away from each other for a long time. Last year a group of German students went to England for a holiday. Their teacher told them that the English people hardly shake hands. So when they met their English friends at the station, they kept their hands behind their backs. The English students had learned that the Germans shake hands as often as possible, so they put their hands in front and got ready to shake hands with them. It made both of them laughs. 1. It is ____ if you know the language and some of the customs of the country. A. not useful        B. not helpful       C. very helpful       D. very bad 2. English people usually shake hands when they ______. A. meet every time                   B. meet for the first time C. say goodbye to each other           D. say hello to each other 3. Usually English people don’t shake hands _______. A. when they will be away for a long time B. when they say “How do you do?” C. when they just meet or say goodbye D. after they haven’t met for a long time 4. Which of the statement（陈述）is right? A. German people shake hands as often as possible. B. English people like shaking hands very much. C. German people hardly shake hands. D. Neither English people nor Germans like shaking hands. 5. This story is about _______. A. shaking hands               B. languages C. customs                    D. languages and customs