如图，△ABC的3个顶点都在⊙O上，AD是△ABC的高，AE是圆的直径，AB=AC=,AD=,则圆的半径是
计算：=_____．
=_____．
约分：=．
化简=_____．
计算：=______；=______．
AC=
,AD=
,则圆的半径是 
=_____．
=_____．
=．
=_____．
=______；
=______．
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