# Indirect Measurement - Using Similar Triangles

Related Topics:
More Lessons for Grade 8 Math
Math Worksheets

Examples, solutions, videos, worksheets, stories, and songs to help Grade 8 students learn about indirect measurement (using similar triangles).

Indirect Measurement Using Similar Triangles
Indirect measurement is a method of using proportions to find an unknown length or distance in similar figures.
Two common ways to achieve indirect measurement involve
(1) using a mirror on the ground and
(2) using shadow lengths and find an object's height.
Method 1 measures the person's height and the distances between the person, mirror, and object.
Method 2 measures shadows and the person's height.
Indirect Measurement: Examples
How to apply your knowledge of similar triangles and proportions to model real-life situations and to find unknown measurements indirectly.
Example:
1. A tree outside Ellie's building casts a 125 foot shadow. At the same time of day, Ellie casts a 5.5 foot shadow. If Ellie is 4 feet 10 inches tall, how tall is the tree?
2. Cameron is 5 ft tall and casts a 12 ft shadow. At the same time of day, a nearby building casts a 78 ft shadow. How tall is the building?
3. The Empire State Building is 1250 ft. tall. At 3:00, Pablo stands next to the building and has an 8 ft. shadow. If he is 6 ft tall, how long is the Empire State Building's shadow at 3:00?

Indirect Measurement Using Similar Triangles
Indirect measurement of stadium lights using similar triangles with 3 methods: a mirror, a shadow, and a photograph.

Rotate to landscape screen format on a mobile phone or small tablet to use the Mathway widget, a free math problem solver that answers your questions with step-by-step explanations.

You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.