1. 7-2 Vocabulary
Similar
Similar polygons
Similarity ratio

2. 7-2 Ratios in Similar Polygons
Geometry

3. Similar (~) Polygons
Two polygons with their corresponding angles are congruent and the lengths of corresponding sides are proportional.

4. Determining Similarity
With comparison of polygons
Corresponding angles have to be congruent
Corresponding sides lengths have to be proportional

5. Similarity Ratio
The ratio of the lengths of two corresponding sides of two similar polygons.

6. Writing Similarity Statements
Ex. 1) Trapezoid ABCD is similar to trapezoid PQRS. (ABCD ~ PQRS)
1a)List all the pairs of congruent angles _______, _______, _______,
________
1b) Write the ratios of the corresponding sides in a statement of proportionality.

7. Determining Similarity
Ex. 2) Decide whether the figures are similar. If they are, write the similarity ratio and a similarity statement.6
A.) B.) 9 A B 6
36°6 F G 6 4
2a)yes, 3/2, rectangle ABCD~rectangle FGHI
2b)no
62°62 H I D C

8. Using Similar Polygons
EX. 3)A boxcar has the dimensions shown. A model of the boxcar is 1.25 in. wide. Find the length of the model to the nearest inch.
36.25 ft
boxcar
X in.
5 ins.
9 ft
model
1.25 ins

9. Assignment

10. Theorem 8.1
If two polygons are similar, then the ratio of their perimeters is equal to the ratios of their corresponding side lengths.

11. Using Similar Polygons
Ex. 4) Parallelogram ABCD is similar to parallelogram GBEF. Find the value of y.
Extra Ex. 5