### Theory:

When line segment $$\overline{\rm AB}$$ meets $$\overline{\rm CD}$$ at right angles, then the line segments $$\overline{\rm AB}$$ and $$\overline{\rm CD}$$ are said to be perpendicular.

Perpendicular:
When two line segments meet at right angles to each other, then the two line segments are said to be perpendicular to each other.
Construction of a perpendicular line using a set square
Step $$1$$: Place a ruler on an empty sheet of paper.

Step $$2$$: Draw a line segment $$\overline{\rm AB}$$ using the ruler.

Step $$3$$:  Place a point $$C$$ on the line drawn.

Step $$4$$: Place a vertex of the set square over the point $$C$$.

Step $$5$$: Draw a perpendicular line to $$\overline{\rm AB}$$ through the point $$C$$.

Construction of a perpendicular line using rulers and compasses
Step $$1$$: Place a ruler on an empty sheet of paper.

Step $$2$$: Draw a line using the ruler.

Step $$3$$: Place the point $$C$$ anywhere on the line.

Step $$4$$: With $$C$$ as centre, draw a semi-circle of any radius such that the semi-circle intersects the line at $$A$$ and $$B$$.

Step $$5$$: With any measurement over $$\overline{\rm AB}$$ as radius and with $$A$$ as centre, draw an arc.

Step $$6$$: With the same radius and $$B$$ as centre, draw an arc to intersect the arc drawn already

Step $$7$$: Mark the intersection of the arcs as $$D$$ and join $$C$$ and $$D$$.

Now, we have constructed a line segment $$\overline{\rm CD}$$ perpendicular to the line segment $$\overline{\rm AB}$$.