Answer:
Step-by-step explanation:
Angle 1 is congruent to angle 4 because they obey alternate interior angles theorem. Same applies to angle 2 and angle 5.
Congruent angles have equal measurement hence, angle 1 = angle 4 and angle 2 = angle 5
According to linear postulate, angle 4 + angle CAD = 180°
According to the angle addition postulate, angle 3 + angle 5 = angle CAD
Lastly, applying the substitution property of equality,
Angle 3 + angle 4 + angle 5 = 180
Angle 1 + angle 3 + angle 2 = 180
