如圖,△ABC按逆時針旋轉至△AB′C′的位置,使AC平分BB′.求證:AB′平分CC′.

如圖,△ABC按逆時針旋轉至△AB′C′的位置,使AC平分BB′.求證:AB′平分CC′.

證明:在△ABB′中,AB=AB′,AC平分BB′,∴AC是等腰△ABB′的頂角平分線,即∠BAC=∠B′AC,在△AMC和△AMC′中,∵AC=AC′,∠MAC=∠MAC′,AM=AM,∴△AMC≌△AMC′,∴MC=MC′,故AB′平分CC′.