The prove ∠ 2 ≅ ∠ 3 is completed by Subtraction property of equality in a two column proof
How to complete the proof
We complete the proof using two column proof as follows
Statement Reason
∠ 1 + ∠ 2 = 180 given (definition of linear pair)
∠ 1 + ∠ 3 = 180 given
∠ 1 + ∠ 2 = ∠ 1 + ∠ 3 Substitution property of equality
∠ 2 ≅ ∠ 3 Subtraction property of equality