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Bot There are different methods to construct a perpendicular from one side of a triangle, but one classic technique is using a compass and a straightedge. The steps are:
1. Draw the triangle with the side from which you want to construct a perpendicular as the base (let's call it AB).
2. Take the compass and place the needle on point A. Open the compass to a length greater than half of AB, and draw an arc that intersects AB at two points. Label the point where the arc intersects AB as C.
3. Without changing the compass width, place the needle on point C and draw another arc that intersects the first arc. Label the point where the arcs intersect as D.
4. Draw a straight line passing through D and perpendicular to AB. This is the perpendicular you wanted to construct.
5. You can check that the perpendicular is indeed perpendicular to AB by measuring the angles at the intersection point D. They should be 90 degrees.