如图Rt△ABO中，∠A=30°，OB=2，如果将Rt△ABO在坐标平面内，绕原点O按顺时针方向旋转到OA'B'的位置．（1）求点B'的坐标．（2）求顶点A从开始到A'点结束经

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如图Rt△ABO中，∠A=30°，OB=2，如果将Rt△ABO在坐标平面内，绕原点O按顺时针方向旋转到OA'B'的位置．

（1）求点B'的坐标．
（2）求顶点A从开始到A'点结束经过的路径长．

上一题下一题 0.0难度选择题更新时间:2016-02-19 05:45:49

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解：（1）过点B′作B′D⊥x轴于D，

由旋转的性质知，∠A′=30°，∠A′OB′=60°，OB′=2，OA′=4，
∴OD=OB′cos60°=2× $\frac{1}{2}$

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Many people think that twins are exactly the same. But some of them are not! Al and Mike are twin brothers. They look the same and in some ways they are the same. But in other ways they are different. Al and Mike are both very strong. Al and Mike both like soccer. But Al plays soccer every day and Mike plays soccer only on weekends. Mike likes watching soccer games on TV but Al only likes to play the game, not to watch it. Al and Mike are both outgoing and funny, but Mike is a little more outgoing than Al. Mike is also a little more serious about school. Al and Mike are very popular at school, and they both have a lot of friends.

根据短文内容判断正误.

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