Question

I need help on which construction is illustrated in the attachment below ?

Answer 1

A perpendicular to a given line from a point not on the line.

Explanation:

The "given line" is in black. A circle is drawn with the center on the the line (light blue interior arcs). Another circle of a larger radius is drawn from each of the points of the first circle's intersection with the line. The intersection of those arcs (light blue, outside the circle) defines the point directly perpendicular to the original point chosen on the line.

Drawing a line from this point to the circle center point on the line will create a perpendicular line from a point not on the line.