Fundamental Concepts
4. The Ray's Journey · One fixed start, infinite direction
The shape always starts at O and passes through A.
A ray starts at a single endpoint (O) and extends infinitely in one direction through another point (A). Drag O to move the starting point; drag A to change the direction. The ray never goes back past O.
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For subscribers · Selina ICSE: Fundamental Concepts
What this lesson covers
Try to break it
Drag O and A around. Watch how the ray always starts at O and follows A. It has only one fixed end!
How you build it
Draw a ray from O through A.
- Click the Point tool and place the starting point O (the ray will start here).
- Place a second point A to show the direction the ray will travel.
- Click the Ray tool, click O, then click A. From O the ray heads toward A and keeps going forever in that direction.
The proof, step by step
A ray has exactly one fixed endpoint. It extends infinitely in one direction and cannot be measured.
- A ray has exactly one fixed endpoint.
- A ray extends infinitely in one direction.
- A ray is a part of a line.
Worked example
A ray is a part of a line that has...
A ray has one fixed endpoint and extends infinitely in one direction, so it cannot be measured.
- Two endpoints.
- One fixed endpoint and extends infinitely in one direction. — correct
- No endpoints.
- Two fixed endpoints.