The vertex is the common endpoint when two rays intersect to form an angle. The formed angle is named by using three points. One point is on each of the two rays, and the third is at the vertex point.
Rays are parts of lines that have one endpoint and extend in one direction indefinitely. In geometry, rays are important because they form angles when they intersect. However, there is a convention used that requires an angle to be named in a particular order. For example, an angle using points D, E and F in which E is the vertex and D and F are points on each ray may be referred to as angle DEF or angle FED, but the vertex (E in this case) must always be in the center of the letters.
Different types of angles may be formed by the intersection of two rays, such as acute, obtuse, right or straight angles. Another possibility is a reflex angle, which is an angle that measures more than 180 degrees. Other angles used in geometry are complementary, supplementary, adjacent and vertical angles. Complementary are two angles with measurements that must add up to 90 degrees, while supplementary angles are two angles with measurement that sum up to 180 degrees.