Let’s take an example

Given a line
l
with point P not on it
2.Place set square on the line so that line is exactly above the setsquare

Put ruler on the hypotenuse side of the set square

Keeping the ruler in the same position,
slide the setsquare till one end of the setsquare passes through point P

Draw a line along the edge of the set square, keeping setsquare firm
Let the line intersect line l at Q
Thus, PQ is the perpendicular to l