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7.2 Similar Polygons • Similar figures – have the same shape but not necessarily the same size. – You can abbreviate is similar to with the symbol ~ . • Two polygons are similar polygons if corresponding angles are congruent and if the lengths of corresponding sides are proportional. Scale Factor • When three or more ratios are equal, you can write an extended proportion. • A scale factor is the ratio of corresponding linear measurements of two similar figures. Understanding Similarity • Triangle MNP ~ Triangle SRT. A. What are the pairs of congruent angles? B. What is the extended proportion for the ratios of corresponding sides? M S , N R, P T MN NP MP SR RT ST Determining Similarity • To determine if figures are similar, you must make sure the corresponding sides are proportional. • You must be able to identify a scale factor and write a similarity statement. Use Similar Polygons • ABCD ~ EFGD. What is the value of x? A. 4.5 B. 5 C. 7.2 D. 11.25 FG ED BC AD x 6 7.5 9 9 x 45 x5 Scale • In a scale drawing, all lengths are proportional to their corresponding actual lengths. • The scale is the ratio that compares each length in the scale drawing to the actual length. More Practice!!!!! • Homework – Textbook p. 444 – 445 #9 – 20.