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.

Answer: The angles shown in the first figure (a) are vertical angles.

Let us understand how to identify vertical angles which are also known as vertically opposite angles.

Explanation:

When two lines intersect, the angles formed opposite to each other are termed as vertical angles.

(a) In the first figure, ∠1 and ∠2 are not adjacent angles. So, ∠1 and ∠2 are vertical angles.

(b) In the second figure, ∠1 and ∠2 are adjacent angles. So, ∠1 and ∠2 are not vertical angles.

So, the pair of angles in the first figure (a) are vertical angles.