Doug C. answered 10/03/22
Math Tutor with Reputation to make difficult concepts understandable
∠5 and ∠6 are vertical angles (def of vertical angles)
∠5≅∠6 (vertical angles are congruent).
Repeat above steps for ∠7and ∠8
Now:
∠6≅∠7 (given)
At this point various ways to get to final statement, depending.....
But note that we have:
∠5≅∠6≅∠7≅∠8
So by transitive property for congruence the following can be deduced:
∠5≅∠8 (that which was to be proved, Q.E.D.)