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平行线间的折线所成的角有以下两种情况:(1)凹进去的模型如图1,若连接AC,则AC在∠BAE和∠ECD之外;(2)凸出来的模型如图2,若连接AC,则AC在∠BAE和∠ECD的内部.解法:从折点处引平行线,即可发现解题思路.例1如图3,AB∥CD,下列结论中正确的是( )(A)∠1+∠2+∠3=180°.(B)∠1+∠2+∠3=360°.(C)∠1+∠3=2∠2.(D)∠1+∠3=∠2.
The angle formed by the polyline of parallel lines has the following two cases: (1) The concave model is shown in Fig. 1, if AC is connected, AC is outside ∠BAE and ∠ECD; (2) 2, if AC, AC in ∠BAE and ∠ECD internal solution: from the breakpoint at the parallel line, you can find solutions to problems. Example 1 Figure 3, AB ∥ CD, the following conclusion is correct () (A) ∠1 + ∠2 + ∠3 = 180 ° (B) ∠1 + ∠2 + ∠3 = 360 ° (C) ∠1 + ∠3 = 2∠2. + ∠3 = ∠2.