When a line and a line segment meet, they form two angles that are each less than 180
degrees. These angles share an endpoint and a side, which makes them adjacent angles.
These angles are called a linear pair because they're made from the same line. Linear pairs
are always supplementary because a line measures 180 degrees, so the two angles formed
from it must measure 180 degrees together.
Angles 1 and 2 below are a linear pair. If angle 1 measures 40 degrees, what is the
measurement of angle 2?
A. 40 degrees
B. 50 degrees
C.120 degrees
D. 140 degrees