### Theory:

A line segment is bounded by two fixed endpoints. A line segment can be constructed:
• Using ruler alone.
• Using a ruler and a compass.

Using a ruler alone:

Problem: Construct a line segment of length $$3.5$$ $$cm$$ using a ruler.

Step 1: A ruler is taken, and zero is marked at one end. Let this point be marked as $$A$$.

Step 2: The other point is marked at the required length, that is, $$3.5$$ $$cm$$. Let this point be marked as $$B$$.

Now, $$AB$$ is the required line segment.