Geometry starts with the most basic building blocks: points, lines, and rays!
Geometry is built on fundamental parts. A POINT is an exact location with no size. A LINE goes on forever in BOTH directions. A LINE SEGMENT has two endpoints — it starts and stops. A RAY has one endpoint and goes on forever in ONE direction. An ANGLE is two rays sharing an endpoint (the vertex).
Line (∞ in both directions)
Line Segment (has endpoints)
Ray (∞ in one direction)
Line segments are the most common in everyday shapes — every side of a polygon is a line segment!
Parts of an angle:
The two rays meet at the vertex. We measure the opening between them in degrees.
Think of the clock hands as two rays starting from the center. At 3:00, the hands form a RIGHT angle (90°). At 6:00, the hands form a STRAIGHT angle (180°). At 12:00, the hands overlap — the angle is 0°!
How to name an angle:
Remember This!
Remember: a LINE has no endpoints (it keeps going), a SEGMENT has two (it stops on both ends), and a RAY has one (it starts but never stops on one side). Like the sun's rays — they start at the sun and keep going!
Which geometric figure has exactly ONE endpoint and goes on forever in one direction?