Vertical angles are a pair of opposite angles formed by intersecting lines.
In the figure, ∠ 1 and ∠ 3 are vertical angles. So are ∠ 2 and ∠ 4 .
Vertical angles are always congruent . So, in this figure, ∠ 1 ≅ ∠ 3 and ∠ 2 ≅ ∠ 4 .
