Question 901564
  "    A linear pair of angles is formed when two lines intersect. Two angles are said to be linear if they are adjacent angles formed by two intersecting lines. The measure of a straight angle is 180 degrees, so a linear pair of angles must add up to 180 degrees." The definition is from google search but don't worry because the definition is correct

So according to the definition of a linear pair, it is formed when two lines intersect and that their angles are adjacent . So it will look like this...
*[illustration image.jpg] .




And the sum of both angles (1 and 2) must be equal to 180 degrees.