3.1+Identifying+Similar+Figures

Marcello Kim 10-16-2008 Block C BI: Many things in our world are mathematically similar and we can use this to understand and describe the world around us.  EQ 3 How can I use math to check if two figures are similar? Question: Examine the four sets of polygons on Labsheet 3.1. Two shapes in each set are similar, and the other is an impostor. In each set, which polygons are similar? Explain your answers, You may cut out polygons if it helps you think about the question.** Parallelogram Set: Shape A is the impostor. Keeping simple: Shape A does not have the same angles as shape B and C. Shape A angles= 135º, 45º,135º, 45º. Shapes B,C=65º,115º,65º, 115º. Decagon Set: Shape B is the impostor. First, it's not a regular decagon as the others. Second, it does not have same ratio for the width/length of shape A and C.(1/1 or 1) Star Set: Shape C is the impostor. The angles (35º, 250º, and so on with the other angles) don't match and also, its not the same ratio for the corresponding sides.(A/B=1/3 for all other sides 1. Question: For each pair of similar figures on Labsheet 3.1, tell what # the side lengths of the small figure must be multiplied by to get the side lengths of the large figure. (You learned that this # is the scale factor from the small to the large figure.)** Parallelogram Set: B-C= The scale factor is 2 Decagon Set: A-C= The scale factor is 3 Star Set A-B= The scale factor is 3 Parallelogram Set: B-C= The scale factor is 0.5 Decagon Set: A-C= The scale factor is 0.333.... Star Set A-B= The scale factor is 0.3333...
 * Problem 3.1: Identifying similar figures**
 * [[image:Untitled.png width="8" height="23"]][[image:mkshapes3.1.png]]
 * Answer:** Rectangle set: Shape B is the impostor. They all have the same angles (90º) and somewhat similar, shape, but shape B did not have the same ratio (2/3 or 0.66) for the width/length.
 * 3.1 F.U
 * Answer:** Rectangle set: A-C= The scale factor is 4
 * 2. Question: For each pair of similar figures on Labsheet 3.1, tell what # the side lengths of the large figure must be multiplied by to get the side lengths of the small figure. (You learned that this # is the scale factor from the large to the small figure.)**
 * Answer:** Rectangle Set: A-C= The scale factor is 0.25
 * 3. Question: How are the scale factors in part 1 and 2 related?**
 * Answer:** They're the opposites. Example: large-small=4, then... small-large=1/4 or 0.25