Question

prove that angle adc is equal to angle A + Angle B + angle C

Answer 1

ABCD is a cyclic trapezium with AB parallel to DC. Given <CAB = 28.

ABC is a right angled triangle, so <ACB = 90 deg, and <ABC = 90–28 = 62 deg. <ABC + <ADC = 180, 62+<ADC = 180 so <ADC = 180–62 = 118 deg.

<ACD = <CAB = 28 deg as AB parallel to DC. So <CAD = 180 - 118–28 = 34 deg. Difference between <ADC and <ABC = 118 - 62 = 56 deg.