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在解(证)圆的题目时,辅助线是关键.那么,应该如何添加辅助线呢?下面我根据不同类型的特点总结了一些常见的辅助线的添加法.1.当题目的已知中有直径的条件时,常常作直径所对的圆周角,然后利用直径所对的圆周角是直角来寻找证题的途径.例1如图1,在△ABC中,∠B=90°,以AB为直径的⊙O交AC于点D,过点D的⊙O的切线DE交BC于点E.求证:BE=EC.
So, how to add the auxiliary line? Now I summarize some common auxiliary line adding method according to different types of characteristics .1. When the title is known Diameter conditions, often for the diameter of the circle around the angle, and then use the diameter of the circle around the angle is a right angle to find the way to prove. Example 1 Figure 1, △ ABC, ∠ B = 90 ° to AB for the diameter of the ⊙ O AC AC at point D, the point D over the ⊙ O tangential intersection BC at point E. Verify: BE = EC.