So ∠B=∠BAD ∠C=∠CAE (internal angles are equal)

Because DE is a straight line, ∠ bad+∠ a+∠ CAE = 180. . . .

2. Do it yourself, minus 180.

Make two horizontal auxiliary lines at two points where A and B intersect at 3.90 degrees, and mark all angles. Combining the principle of balance line, the sum of internal angles of triangle and the degree of right angle, we can get ∠ cab = 30 ∠ CBA = 60 ∠ BCA = 90.