1. B A C D E 9m 13m 50m river A new bridge is going to be built across a river, but the width of the river cannot be measured directly. Find the width of the river. The triangles are similar, so set up a proportion to determine AB, the width of the river.

2. Bob is standing beside a lighthouse on a sunny day, as shown. He measures the length of his shadow and the length of his shadow cast by the lighthouse. Bob is 1.6m tall. How tall is the lighthouse? Bob 1.6m 4.8 m 75.0 m Lighthouse

3. 1.6m 4.8 m h 75.0 m The triangles are similar because 2 pairs of corresponding angles are equal.

4. Similar triangles can be used to determine lengths that cannot be measured directly This strategy is called indirect measurement