Answer:
∠1 is supplementary to ∠3.
Step-by-step explanation:
Given information: ABCD is a parallelogram.
Prove: ∠1 is supplementary to ∠3.
Proof:
∠1 = ∠ADB
∠2 = ∠DBC
∠3 = exterior angle adjacent to angle D B C.
Statement Reason
∠2 is supplementary to ∠3 Linear pairs
m∠2+m∠3=180° Definition of supplementary angles
Alternative interior angles
m∠1+m∠3=180° Substitute property of equality
∠1 is supplementary to ∠3 Definition of supplementary angles
Hence proved.
