19. 16 under the root number 15.

D is the height DH of AB side.

Because it is an isosceles trapezoid, AH is 1/2(AB-DC)=2.

According to Pythagorean theorem, DH is 15 under the root sign.

Find the root number of 16 and the area of 15.

20. If you don't know the degree of edc, just talk about your thoughts.

Because angles A and B are complementary, AD is parallel to BC.

Angle C= angle ADC = 90

Angle ADE from angle edc

Angle ADE and angle a are complementary.

Therefore, three angles are obtained.