Fundamental Concepts
2. The Infinite Line · Stretching forever in both directions
Point P always stays on the line, no matter how far you drag it.
A line extends infinitely in both directions — no endpoints, no thickness, perfectly straight. The arrows on each end remind us it never stops. Drag P along the line to see it always stays on this single straight path.
Stuck? Ask Guru
For subscribers · Selina ICSE: Fundamental Concepts
What this lesson covers
Try to break it
What if we put a stop sign on the line? It would become a line segment with a definite length. But a true line never stops—it has no endpoints and no thickness, only length.
How you build it
Draw a line through two points.
- Click the Point tool and place point A somewhere on the canvas.
- Click the Point tool again and place point B in a different spot.
- Click the Line tool. Click once near A, then click near B — the line is drawn through both points and stretches as far as the canvas allows.
The proof, step by step
Prove that the figure is a line that extends endlessly in both directions.
- A line has only length. It has no width or thickness.
- A line extends infinitely in both directions, shown by arrows at both ends.
- A line is uniquely determined by any two distinct points on it.
Worked example
According to the definition of a line, which of the following statements is always true?
A line is a one-dimensional object that extends infinitely in both directions. It has length but no width or thickness.
- It has both length and width.
- It extends infinitely in both directions and has only length. — correct
- It has a definite length and two endpoints.
- It has thickness but no width.