As shown in the figure, fold the paper triangle ABC along de. when point a falls inside the quadrilateral BCDE, what is the relationship between angle A and angle 1 plus angle 2? Explain the reason

As shown in the figure, fold the paper triangle ABC along de. when point a falls inside the quadrilateral BCDE, what is the relationship between angle A and angle 1 plus angle 2? Explain the reason

（1）2∠A=∠1+∠2；
(2) In the original triangle ABC, a + B + C = 180 ° 1;
In △ ade, ∠ a + ade + AED = 180 ° ②;
In the quadrilateral BCDE, ∠ B + ∠ C + ∠ 1 + ∠ 2 + ∠ ade + ∠ AED = 360 ° ③;
① 2 ∠ a = 1 + 2 from + 2 - 3;
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