(1)∠2 is an angle of 90, that is, AE is perpendicular to EF.

Let BE, CE and EG overlap, which can be seen from origami.

∠ 1=∠AEG，∠3=∠FEG

∴∠ 1+∠3=∠AEG+∠FEG

∴∠ 1+∠3+∠aeg+∠feg= 180

∴∠1+∠ 3 = ∠ AEG+∠ Feg =180, that is, ∠ 2 = 90.

Complementarity: ∠3 and ∠ 1 ∠3 and ∠EFC ∠ 1 and ∠EAB

Complementarity: ∠D and ∠ C. D and B. D and a. C and B. C and a. B and a.