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.
 
fig_16.svg
 
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.
 
ruler_2.png
 
Step \(2\): Draw a line segment \(\overline{\rm AB}\) using the ruler.
 
fig_2.png
 
Step \(3\):  Place a point \(C\) on the line drawn.
 
fig_3.png
 
Step \(4\): Place a vertex of the set square over the point \(C\).
 
measure_6.png
Step \(5\): Draw a perpendicular line to \(\overline{\rm AB}\) through the point \(C\).
 
fig_16.svg
 
Construction of a perpendicular line using rulers and compasses
Step \(1\): Place a ruler on an empty sheet of paper.
 
ruler_2.png
 
Step \(2\): Draw a line using the ruler.
 
measure_1_1.png
 
Step \(3\): Place the point \(C\) anywhere on the line.
 
fig_4.png
 
Step \(4\): With \(C\) as centre, draw a semi-circle of any radius such that the semi-circle intersects the line at \(A\) and \(B\).
 
fig_5.png
 
Step \(5\): With any measurement over \(\overline{\rm AB}\) as radius and with \(A\) as centre, draw an arc.
 
fig_6_1.png
 
Step \(6\): With the same radius and \(B\) as centre, draw an arc to intersect the arc drawn already
 
fig_7.png
 
Step \(7\): Mark the intersection of the arcs as \(D\) and join \(C\) and \(D\).
 
fig_8.png
 
Now, we have constructed a line segment \(\overline{\rm CD}\) perpendicular to the line segment \(\overline{\rm AB}\).