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如图，某校综合实践活动小组的同学欲测量公园内一棵树DE的高度，他们在这棵树正前方一座楼亭前的台阶上A点处测得树顶端D的仰角为30°，朝着这棵树的方向走到台阶下的点C处，测得树顶端D的仰角为60°．已知A点的高度AB为2m，台阶AC的坡度为1： 3 ，且B，C，E三点在同一条直线上．请根据以上条件求出树DE的高度（测倾器的高度忽略不计）．
上一题 下一题 0.0难度 选择题 更新时间:2019-08-17 09:44:29

答案(点此获取答案解析）

解：∵AF⊥AB，AB⊥BE，DE⊥BE，

∴四边形ABEF为矩形，

∴AF=BE，EF=AB=2

设DE=x，在Rt△CDE中，CE= DEtan∠DC

同类题1

阅读理解(A)
    My friend，Victor，is a zoo keeper in the National Zoo．His work is very interesting but it is hard．Sometimes it is dangerous，too．Every morning，the zoo keepers have to get up at five to prepare the food for the animals．Each kind of animal eats special food．For example，the lions must be given meat； the deer must be given grass and leaves； and the parrots must be given fruit and nuts．Sometimes some animals won't let the others eat their food．If this happens，each of them must be fed separately（分离的）．
    Every morning each cage （笼子） must be washed by the zoo keepers．This can be dangerous，especially with lions and tigers．To make the work easier，the animals are locked in the sleeping compartments（ 隔间） while the cages are being washed．When the animals are sick，the zoo keepers must look after them．Each sick animal is kept in a separate cage and given medicine．Sometimes they must be given injection．It is not easy to inject a sick lion!
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    The most important job of the keepers is to look after the safety of the visitors．People must be stopped from doing dangerous things．Many people have been hurt because they did careless things，like putting their hands into the lion's cage．

同类题2

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已知函数f（x）=x2+ 2(m−1)x+m4 ，现有一组数据，绘制得到茎叶图，且茎叶图中的数据的平均数为2．（茎叶图中的数据均为小数，其中茎为整数部分，叶为小数部分）

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“芒果黄了叫人爱，芭蕉熟了任你采，菠萝大了任你 摘……”这首歌词描绘的地方，其气候类型属于(    )

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