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5. AB is a line segment of required length 4.5 cm.

l
4.5 cm
A B
Constructing a Copy of a Given Line Segment

To construct a copy of a given line segment, we can measure the length of the given line segment
and then draw a line segment of the same length using a ruler.
Let us construct a copy of a line segment AB without measuring AB .

For this, we need to construct another line segment PQ, which is of the same length asAB .
Steps of construction:

1. Draw a line l. Mark a point P on it. P l
2. On the given line segment AB , place the pointer of the compass on point A and the pencil
point on B.

A B
3. Without changing the opening of the compass, place the pointer on P and draw an arc to
cut l at Q.

l
P Q
4. Hence, PQ is the copy of AB. That is, AB = PQ.

Example 1: Draw a line segment AB of length 6.2 cm. From this, cut a line segment AC of length
3.7 cm. Measure BC .

Solution: Steps of construction:
A 6.2 cm B
1. Draw a line segment AB of length 6.2 cm.
2. Place the pointer of the compass on the zero-mark of the ruler.

3. Open the compass to place the pencil upto 3.7 cm mark.
4. Without changing the measure, place the point of the compass on A and draw an
arc that cut. AB at C.

333 Construction of Basic Geometrical Shapes