共50条信息
如图,\(\triangle OAB\)是等腰三角形,\(∠AOB=120^{\circ}.\)以\(O\)为圆心,\(\dfrac{1}{2}\)\(OA\)为半径作圆.
\((I)\)证明:直线\(AB\)与\(⊙O\)相切
\((II)\)点\(C\),\(D\)在\(⊙O\)上,且\(A\),\(B\),\(C\),\(D\)四点共圆,证明:\(AB/\!/CD\).
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