摘要：26．已知.如图:直线AB.CD被直线EF所截. Ð 2 = Ð3.求证Ð 3 + Ð4 = 180° 证明: ∵Ð 1和Ð 2是对顶角 ( ) ∴Ð 1 = Ð 2 ( ) ∵Ð2 = Ð 3 ( ) ∴Ð 1 = Ð 3 ( ) ∵Ð 1 + Ð 4 = 180° ( ) ∴Ð3 + Ð 4 = 180° ( )

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