Question

in which diagram do angles 1 and 2 form a linear pair?

Explanation:

Step1: Recall linear - pair definition

A linear pair of angles is a pair of adjacent angles whose non - common sides are opposite rays and whose sum is 180 degrees.

Step2: Analyze first diagram

In the first diagram, angles 1 and 2 are vertical angles (opposite angles formed by the intersection of two lines), not a linear pair.

Step3: Analyze second diagram

In the second diagram, angles 1 and 2 are adjacent, and their non - common sides are opposite rays. So, they form a linear pair.

Answer:

The second diagram.