Optical tricks often intrigue us. In reality a little math can often explain exactly why they work. In the picture above the only math needed to figure out how far one must stand from the Lincoln Memorial in order to view the real life figure and the picture on the bill as the same size is triangle similarity and manipulation of proportions. One must also know how tall the real memorial is, how large the picture on the $5.00 bill is, and how far they are holding the bill from their eyes. The following is a diagram of the similar triangles that can be used to calculate how far you are from the Memorial where the bill and the memorial are Parallel:

This problem satisfies the CCSS’s HSG.MG.A.1. and HSG.SRT.B.5 which are, “Use geometric shapes, their measures, and their properties to describe objects,” and “Use congruence and similarity criteria for triangles to solve problems and to prove relationships in geometric figures,” respectively.