7.2 Similar Polygons Pg 365 Objective: Students will use proportions to identify similar polygons.

Similar polygons Similar polygons- 2 polygons that have  corresponding  s and proportional corresponding side lengths. AB C D W X Y Z ABCD~WXYZ

Trapezoid ABCD~ Trapezoid WXYZ. List all the pairs of   s and a statement of proportionality of the ratios of the corresponding sides AWBXCYDZAWBXCYDZ AB CD W X YZ

Example decide whether the Δs are ~. A B C X Z Y __ ) )) ) Yes, because all corresponding  s are  and there is a ratio of 1:3 between all pairs of corresponding sides.

Example cont. L M N P Q R Not ~ because not all the corresponding  s are  ( )

Scale Factor Scale factor- the ratio of the lengths of 2 corresponding sides of ~ polygons. __ 12in 36in 126in 42in The 2 pics are ~, what is the scale factor? enlargement painting

Example cont. What would the ratios of the perimeters be? 2(12)+2(36)=96 2(42)+2(126)=336

Thm 6.1Perimeters of similar Polygons. If 2 polygons are ~ then the ratio of their perimeters is = to the ratio of their corresponding lengths Ratio of perimeters = scale factor

Example: parallelogram ABCD ~ parallelogram GBEF. Find the value of y and the ratio of the perimeters. B G A E F C D Y y=288 y=19.2 Ratio of Perimeters = 5/8

Go to guided Practice! Pg 648

Assignment Page #8-26even.