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(2000•兰州)如图,在Rt△ABC中,∠A=90°,AB=AC=a,⊙O分别...
(2000•兰州)如图,在Rt△ABC中,∠A=90°,AB=AC=a,⊙O分别与AB、AC相切于E、F点,圆心O在BC上,则⊙O的半径等于( )
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232724992388113/SYS201310212327249923881000_ST/images0.png)
A.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232724992388113/SYS201310212327249923881000_ST/0.png)
B.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232724992388113/SYS201310212327249923881000_ST/1.png)
C.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232724992388113/SYS201310212327249923881000_ST/2.png)
D.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232724992388113/SYS201310212327249923881000_ST/3.png)
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