Answer:
See the answer below.
Step-by-step explanation:
∠ a and ∠c are vertical angles Given
∠a + ∠d = 180 Definition of linear pairs or straight angles
∠d + ∠c = 180 Definition of linear pairs or straight angles
∠a + ∠d = ∠d + ∠c Substitution
∠a = ∠c Subtraction
Therefore ∠a ≅ ∠c Definition of congruent
Note:
Now you know that if you have a pair of vertical angles then the angles are congruent
