In which diagram are angles 1 and 2 vertical angles?
Vertical angles are a pair of non-adjacent angles formed by the intersection of two straight lines.
Vertical angles are located across from one another in the corners of the "X" formed by two straight lines.
(a) Clearly, ∠1 and ∠2 are not adjacent angles. So, ∠1 and ∠2 are vertical angles.
(b) Clearly, ∠1 and ∠2 are adjacent angles. So, ∠1 and ∠2 are not vertical angles.