A. Through each vertex draw a line perpendicular to the line of reflection.
B. Measure the distance from each vertex to the line of reflection. Locate the image of each vertex on the same side of the line of reflection and the same distance from it.
C. Connect the pre-images of the vertices.
D. Measure the distance from each vertex to the line of reflection. Locate the pre-image of each vertex on the opposite side of the line of reflection and the same distance from it.