Question

Practice identifying angle relationships.
Explain the different ways you can name an angle. What are the different names for this angle?

Lines R S and S T combine to form angle 1.

Answer 1

When two rays meet at a vertex you can name the angle several ways. Here the rays are SR and ST, so the vertex is S and the angle formed is angle 1.

Valid names for that same angle:
- ∠RST (three-letter name: first point on one ray, vertex S, a point on the other ray)
- ∠TSR (the same three letters in the opposite order)
- ∠S (single-letter name — only if there is just one angle at S; otherwise avoid because it can be ambiguous)
- ∠1 (using the given number label)
- m∠RST or m∠1 (to denote the measure of the angle)

Reminder: when using three letters the middle letter must be the vertex (S).