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对于某些几何证明题，如果已知条件中出现了三角形的一个内角是另一个内角的两倍．或者已知条件中出现了用的平分钱．那么解答这类问题时，我们可以考虑构造等腰王角形来进行证明．例1如图卜在西ABt”中．上Al］L”。－－2二t”．AD二BC”于从求证：AB＋BI7一IK”．证明延长DB
For some geometrical proofs, if one of the internal corners of the triangle is known to be a condition that is twice the internal angle. Or the equal amount of money used in the known conditions. When answering this kind of question, we can consider constructing an isosceles king shape to prove it. Example 1 is shown in Fig. B. In the west ABt“. Al”L“. - 2 two t”.AD two BC“ from Proof: AB+BI7 an IK”. Prove to extend DB