北师大九年级下《圆》单元评估试卷(B)
13.如图,A,B,C三点在⊙O上,且AB是⊙O的直径,半径OD⊥AC,垂足为F,若∠A=30º,OF=3,则BC=__________.
14.如图为直径是52cm圆柱形油槽,装入油后,油深CD为16cm,那么油面宽度AB=_________cm.
15.△ABC的三个顶点在⊙O上,且AB=AC=2,∠BAC=120º,则⊙O的半径=_________,BC=_________.
16.如图, ⊙O中弦AB⊥AC,D,E分别是AB,AC的中点.若AB=AC,则四边形OEAD是_________形;
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