How to Copy an Angle without a Compass

In this video, Chris Tisdell shows how to copy a given angle CDE onto a given line segment AB. He uses a circle arc template and a straightedge. He forms an isosceles triangle whose base angle is angle CDE and has base DF. He then cuts off a segment AE from AB that is equal to DF. Finally, AE is bisected, forming a triangle that is congruent to the original triangle. This means that the corresponding angles to each triangle are equal and so we have copied the original angle over.