1. BASIC GEOMETRY Section 7.5: Using Proportional Relationships

2. Indirect Measurement
Method to use formulas, similar figures, and/or proportions to measure objects that are hard to directly measure
One method is to use the angle of the sun and shadows that are cast to measure tall things.
height
shadow

3. Example 1
A student who is 5ft 6in tall measured shadows to find the height of a flagpole. The shadow on the flagpole was 14ft 2in and the student’s shadow was 5ft. Find the height of the flagpole.

4. Scale Drawings A way to represent objects at a different size
Scale = ratio of drawing to actual =

5. Example 2:
On a Wisconsin road map, Kristin measured a distance of 11 1/8 in from Madison to Wausau. The scale of this map is 1 in: 13 miles. What is the actual distance between Madison and Wausau to the nearest mile?

6. Example 3
Lady Liberty holds a tablet in her left hand. The tablet is 7.19 m long and 4.14 m wide. If you made a scale drawing using the scale 1 cm:0.75 m, what would be the dimensions to the nearest tenth?

7. Similarity, Perimeters, & Areas3 5

8. Proportional Perimeters & Area Thm
If similarity ratio of two similar figures is , then
The ratio of the perimeters =
The ratio of the areas =

9. Example 4
∆ABC ∼ ∆DEF, BC = 4 mm, and EF = 12 mm. If P = 42 mm and A = 96 mm2 for ∆DEF, find the perimeter and area of ∆ABC.

10. Assignment #5
Page 491 #’s 1-11,(52)