Course Guide - USAID Teacher Education Project

Unit 3 GeometryWeek 1, Session 3: Introduction to Similarity, Reference Angles1. What are the important concepts?a) Similar figures are those whose side lengths are in direct proportion to each other,with the corresponding angles equal in degrees. Consider this drawing of a tiger:The larger drawing resulted by using a “scale factor” of 2, doubling both the lengthand the width of the original picture.When dealing with geometric shapes (which are far simpler than the drawing of thetiger) each side of the figure is multiplied by the same scale factor while thecorresponding angles remain the same. Look at this example of a regular pentagonthat retains its shape regardless of the scale factor used:b) Scale factors are just that: factors. As such, the operations used when creatingsimilar figures are multiplication and division (or multiplying by a scale factor lessthan 1).c) The mathematical sign to indicate that two shapes are similar is ~ . Thus the finalsentence for the first set of diagrams would be read, "Figure ABCD is similar to