△ADE folds along point e, and point a coincides with point d.
. . △AFE?△DFE
Ae = ed: af = FD ∴ f is the midpoint of AD, that is, EF is the midline of △AEF.
∵ EF⊥AD ∴ △AEF is an isosceles right triangle.
< < a is 45.
Ps: It seems certain ~ ~ ~ Then ps: This sogou really has everything (O. O) ||||||| Always feels that he is hurting his friends.