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初中数学八年级上册试题库(555题)


如图,在等边ABC外侧作射线APBAP=\(\alpha \),点B关于射线AP的对称点为点D,连接CDAP于点E,连接BE


\(0^\circ < \alpha < 60^\circ \)时,用等式表示线段AECDDE之间的数量关系,并证明。



知识点:第十三章 轴对称


参考答案:


\(CD = 2DE + AE\)



证明:如图,在\(CD\)上截取\(BG = BE\)





\(\because \angle BEC = 60^\circ \)



\(\therefore \Delta BGE\)是等边三角形,



\(\therefore \angle BGC = \angle AED = 120^\circ \)



\(\because \angle BCE = \angle DAE = \alpha \)



\(\therefore \Delta BCG \cong \Delta DAE(AAS)\)



\(\therefore AE = CG\)



\(\because EG = BE = DE\)



\(\therefore CD = 2DE + CG\)



\(CD = 2DE + AE\)


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