1. Similar Figures
The Big and Small of it

2. For Polygons to be Similar corresponding angles must be congruent, and corresponding sides must be proportional (in other words the sides must have lengths that form equivalent ratios)

3. Congruent figures have the same size and shape
Congruent figures have the same size and shape. Similar figures have the same shape but not necessarily the same size. The two figures below are similar. They have the same shape but not the same size.

4. Let’s look at the two triangles we looked at earlier to see if they are similar. Are the corresponding angles in the two triangles congruent? Are the corresponding sides proportional? (Do they form equivalent ratios)

5. Just as we solved for variables in earlier proportions, we can solve for variables to find unknown sides in similar figures. Set up the corresponding sides as a proportion and then solve for x.
Ratios
x/12
and
5/10 x
10x = 60
x = 6

6. Determine if the two triangles are similar.

7. In the diagram we can use proportions to determine the height of the tree. 5/x = 8/28 8x = 140 x = 17.5 ft

8. The two windows below are similar
The two windows below are similar. Find the unknown width of the larger window.

9. These two buildings are similar. Find the height of the large building.