When two straight lines intersect, four angles are formed. If the line is 180 degrees, each pair of angles that are adjacent to each other are most likely linear pair angles. The two angles must contain measurements that add up to 180 degrees in order for the angles to be linear pairs.
When a linear pair occurs, the two angles might be equal or they might be different. If one of the angle's measurements is 90 degrees, the other angle must also measure 90 degrees, because the sum of both angles must equal 180 degrees. If one of the angles is acute, the other must be obtuse. An acute angle is one that measures less than 90 degrees. An obtuse angle measures greater than 90 degrees. Angles that are 90 degrees are considered right angles.
There are several other types of angle pairs, including adjacent angles. This type of angle pair contains two angles that have a common side and a common vertex, but do not have any common interior points. Vertical angle pairs are formed when two lines intersect. They are the angles that are opposite of each other and not adjacent. Vertical pair angles must be equal in measure. Complementing angle pairs are formed from a 90-degree, or right, angle. Their angle measurements when added together must equal 90 degrees.
When two angles meet the qualifications to form a linear pair, they are also said to be supplementary angle pairs, because supplementary angle pairs also contain a sum of 180 degrees. Not all supplementary angles, however, are placed in the configuration that would make them linear pairs, but typically they are.