7.2 Similar Polygons Two polygons are similar (~) if and only if their Corresponding angles are  and the measures of the corresponding sides are proportional. Same shape but not necessarily the same size.

Small ~ Large Find x & y. 3 8 8x = 24 Cross Multiply 4 x = 3 Divide by 8 – Solve for x. y x 6 8y = 18 Cross Multiply y = 2.25 Divide by 8 – solve for x.

Scale Factor When you compare the lengths of corresponding sides of similar figures, you usually get a numerical ratio. This ratio is called the scale factor for the two figures. The height of the Soldiers’ National Monument in Gettysburg, Pennsylvania is 60 feet. The height of a model is 10 inches. What is the scale factor of the model compared to the original? 1st: Convert 60 feet to inches: 60(12) = 720 inches 2nd: Write a proportion and simplify

Proportional Parts and Scale Factor Write a similarity statement, then find a and the scale factor of the big triangle to the small triangle. K L J X Y Z a in 3 in 2 in 1.5 in Similarity Statement (match up the vertices): Scale Factor: 3/2

Textbook Example Problem similar to p. 391 Example #5

Homework #46 p. 392 8-11, 13-23 odd, 28-40 even, 48, 57-58