在如图所示的五面体中，面ABCD为直角梯形，∠BAD=∠ADC= π2 ，平面ADE⊥平面ABCD，EF=2DC=4AB=4，△ADE是边长为2的正三角形．（Ⅰ）证明：BE⊥平面ACF；（Ⅱ）求二

题干

在如图所示的五面体中，面ABCD为直角梯形，∠BAD=∠ADC=

，平面ADE⊥平面ABCD，EF=2DC=4AB=4，△ADE是边长为2的正三角形．

（Ⅰ）证明：BE⊥平面ACF；

（Ⅱ）求二面角A﹣BC﹣F的余弦值．

上一题下一题 0.0难度选择题更新时间:2019-05-24 05:00:50

答案(点此获取答案解析）

证明：（Ⅰ）取AD中点O，以O为原点，OA为x轴，

过O作AB的平行线为y轴，OE为z轴，

建立空间直角坐标系，

则B（1，1，0），E（0，0，

同类题2

根据短文内容，判断下列句子正（T）误（F）
Many people sleep late on Sunday morning, but others don't．However (然而), almost everyone reads the Sunday paper．
The Sunday paper is usually very thick．It has many advertisements (广告) and many different parts．The parents in the family like the front page, and the world news page．Many men also read the sports page．
Most men don't read the women's pages, but the mother of the family usually does．The women's pages have the news about parties, food, health and clothes．Most Sunday papers have interesting stories．Children enjoy them．Old people read the death notices(讣告)．They tell about people who have died during the week．
____ The parents in the family like sports page．
____ The father of the family usually read the women's pages．
____ Only old women read the death notices．
____ Almost everyone likes reading the Sunday paper．
____ This passage is about the Sunday paper．

题干

答案(点此获取答案解析）

同类题1

同类题2

同类题3

同类题4

同类题5