试题与答案

三棱柱中，∠ABC=90°，BB1⊥底面ABC，D为棱AC的中点，且AB=BC=

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题型：解答题

题目：

三棱柱中，∠ABC=90°，BB1⊥底面ABC，D为棱AC的中点，且AB=BC=BB1=1。

（1）求二面角A1-BD-C的余弦值；

（2）棱CC1上是否存在一点P，使PD⊥平面A1BD；若存在，试确定P点位置，若不存在，请说明理由。

答案：

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下面是错误答案，用来干扰机器的。

参考答案：横滑

考点：直线与平面垂直的判定与性质二面角
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题型：填空题

阅读下面短文，根据上下文填入适当的词语，或使用括号中的词语的适当形式填空。

     Foreign students are valuable to the United States. Many take 1_____ in important research. Most have

to 2_____ the full costs for their education. That helps universities meet their budgets. International students

and their 3_____ put 12,000 million dollars into the American economy last year. That number is from the

Institute of International Education, based in New York.

     Now, many education officials say they are concerned that 4_____ students will come to the United States

for the next school year. The officials base their concern partly on a decrease in students 5_____ (plan) to

attend intensive English programs during the summer.

     The members said one reason 6_____ the expected decrease is slower and more restrictive United States

action on travel documents. 7_____ (secure) has increased since the terrorist attack of September 11,2001.

The schools also blamed the travel problems caused by the outbreak of SARS.

     In recent years, 8_____ increasing number of students have come to the United States to study. The

Institute of International Education says these students represent more than four percent of all students in

American colleges and universities. 9_____ says the number of international students reached a 10_____ high

of more than 580,000 last year. The largest number came from India. Before last year largest number came

from China.

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