Answer + Step-by-step explanation:
AB parallel to CD; GIVEN.
Angle 1 congruent to Angle 5; by CORRESPONDING ANGLES.
Angle 2 congruent to Angle 4; by ALTERNATE INTERIOR ANGLES
Angle 3, Angle 4, Angle 5 are supplementary; GIVEN in image.
Angle 3 + Angle 4 + Angle 5 = 180° by defn of SUPPLEMENTARY.
Angle 3 + Angle 2 + Angle 1 = 180° by SUBSTITUTION.