As shown in the figure, fold the triangle ABC paper along De, when point a falls inside the quadrilateral BCDE, ∠ a, ∠ 1, ∠ 2 When point a falls in the interior of the quadrilateral BCDE, what is the quantitative relationship among the degrees of ﹥ a, ﹥ 1, ﹥ 2? Please write it down and explain why

As shown in the figure, fold the triangle ABC paper along De, when point a falls inside the quadrilateral BCDE, ∠ a, ∠ 1, ∠ 2 When point a falls in the interior of the quadrilateral BCDE, what is the quantitative relationship among the degrees of ﹥ a, ﹥ 1, ﹥ 2? Please write it down and explain why

In △ AEA ′、 △ ADA ′, we can connect AA ′, and use the external angle property of triangles to express ∠ 1 and ∠ 2 respectively. We can get the conclusion by adding the two together and folding them simultaneously
Connect AA ′
Then △ a ′ ED is the triangle before folding,
It is known from the properties of the fold: ∠ DAE = ∠ Da ′ E
It is known from the properties of the external angle of the triangle that:
∠1=∠EAA′+∠EA′A,∠2=∠DAA′+∠DA′A；
Then ∠ 1 + 2 = ∠ DAE + Da ′ e = 2 ∠ DAE,
That is, 1 + 2 = 2 A
So the answer is: 1 + 2 = 2 A