真题
1 . 如图,已知AB是圆O的直径,AB=4,EC是圆O的切线,切点为C,BC=1.过圆心O作BC的平行线,分别交EC和AC于D和点P,则OD=_________ .
![](https://img.xkw.com/dksih/QBM/2015/6/25/1572144872194048/1572144878018560/STEM/ed7e04baa24b4b8aa64e4d12bdfb3c86.png?resizew=206)
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真题
2 . (几何证明选讲选做题)如图,在直角梯形ABCD中,DC∥AB,CB⊥AB,AB=AD=a,CD=
,点E,F分别为线段AB,CD的中点,则EF=_______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/576833b76e9cad3b523f87132308df99.png)
![](https://img.xkw.com/dksih/QBM/2010/6/23/1569766052364288/1569766057615360/STEM/29f92148-c0cd-47f6-81c0-a6073706d036.png)
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