Illustration showing optical illusions. It is not always possible to trust the eye to be sure if the lines are prolongations of the other lines. You may need to measure to be sure of your conclusion.
Keywordsgeometry, optical illusion, measurement, measure, lines, Prolongation, lengths, illusions, prolongations
C. A. Hart & Daniel D. Feldman Plane And Solid Geometry (New York: American Book Company, 1911) 21