Answer:
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Step-by-step explanation:
Given: c is parallel to d and ∠4=∠5.
To prove: ∠7=∠8
Proof:
Statement                         Reason
1. c║d, ∠4=∠5                      Given
2.∠4=∠7                   If lines ||, alternate interior angles are equal.
3.∠5=∠8                       Vertical angles are equal
Since, ∠4=∠5, therefore ∠7=∠8
4.∠7=∠8                        Substitution