题干

下面是“作一个 30° 角”的尺规作图过程.

已知:平面内一点 A .

求作: A ,使得 A=30° .

作法:如图,

①作射线 AB

②在射线 AB 上取一点 O ,以 O 为圆心, OA 为半径作圆,与射线 AB 相交于点 C

③以 C 为圆心, OC 为半径作孤,与 O 交于点 D ,作射线 AD . DAB 即为所求的角.____

请回答:该尺规作图的依据是____

上一题 下一题 0.0难度 选择题 更新时间:2019-04-13 05:43:37

答案(点此获取答案解析)

如图所示:,同弧所对的圆周角等于圆心角的一半

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    “Years ago when I was at the Grand Canyon, I remembered someone coming up to the canyon's edge, taking a shot with a camera and then walking away, like 'got it – done', barely even glancing at the magnificent scene in front of him,” Linda Henkel, a scientist at Fairfield University, US told Live Science.

    Henkel was surprised by how obsessed (痴迷的) people are with taking pictures these days - before dinner, during friends' birthday parties, on museum tours and so on.

    They keep taking pictures because they think that it helps record the moment, but as Henkel's latest study has just found out, this obsession may prevent their brains remembering what actually happened, reported The Guardian.

    In her study, Henkel led a group of college students around a museum and asked them to simply observe 15 objects and photograph 15 others. The next day the students' memory of the tour was tested, and the results showed that they were less accurate in recognizing the objects and they remembered fewer details about them if they photographed them.

    ''When people rely on technology to remember them — counting on the camera to record the event and thus not needing to attend to it fully themselves, it can have a negative impact on how well they remember their experiences,” Henkel explained.

    But there is also an exception: if students zoomed in to photograph part of an object, their memory actually improved, and those who focused the lens (镜头) on a specific area could even recall parts that weren't in the frame.

    So basically, this study is saying that constantly taking pictures can harm your memory. But shouldn't reviewing pictures we have taken help wake up our memories? This is true, but only if we spend enough time doing it.

    “In order to remember, we have to access and interact with the photos, rather than just collect them,” Henkel told The Telegraph. However, previous research has shown that most people never take the time to look over their digital pictures simply because there are too many of them and they aren't usually very organized on their computers.

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