Lesson 9-7 Pages 471-475

Similar Triangles and Indirect Measurement

Lesson Check 9-6

Lesson Check 9-5

What you will learn!1. How to identify corresponding

parts and find missing measures of similar triangles.

2. Solve problems involving indirect measurement using similar triangles.

Similar trianglesSimilar trianglesIndirect measurementIndirect measurement

What you really need to know!

Similar triangles are triangles that have the same shape but not necessarily the same size. If two triangles are similar, then the corresponding angles have the same measure, and the corresponding sides are proportional.

What you really need to know!

The properties of similar triangles can be used to find measurements which aredifficult to measure directly. This is called indirect measurement.

Example 1:

If ∆RUN ~ ∆CAB, what is the value of x?

104

8 x

x480

x20

Example 2:

A surveyor wants to find the distance RS across the lake. He constructs ∆PQT similar to ∆PRS and measures the distances as shown. What is the distance across the lake?

x

12

60

25

x25720

x8.28

m8.28

Example 3:

Suppose the John Hancock Center in Chicago, Illinois, casts a 257.5 foot shadow at the same time a nearby tourist casts a 1.5 foot shadow. If the tourist is 6 feet tall, how tall is the John Hancock Center?

x

257.5 ft

6 ft

1.5 ft

5.1

5.257

6

x

1,5455.1 x

1,030xft030,1

5.1

5.257

6

x

Page 473

Guided Practice

#’s 3-6

Pages 471-473 with someone at home and

study examples!

Read:

Homework: Pages 474-475

#’s 7-18

#’s 21-22, 26, 27, 29-35

Lesson Check 9-7

Page

747

Lesson 9-7

Lesson Check 9-7

Study Guide and Review

Pages

483-485

#’s 1-24, 34-35(Odd answers in back of book)

Prepare for Test!Pages

487

#’s 1-14, 16, 20

Lesson Check Ch-9Lesson Check 9-7

Prepare for Test!Pages

488-489

#’s 1-23