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Using Similar Triangles. Butterflies, Pinwheels and Wallpaper 4.4. Learning Goal 1 (8.G.A.3 & 4): The student will understand and use informal arguments to prove congruency and similarity using physical models, transparencies or geometry software. Similar Triangles.
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Using Similar Triangles Butterflies, Pinwheels and Wallpaper 4.4
Learning Goal 1 (8.G.A.3 & 4): The student will understand and use informal arguments to prove congruency and similarity using physical models, transparencies or geometry software.
Similar Triangles • Similar triangles have the same shape, but are usually a different size. • You can use the relationships between corresponding parts of similar triangles to solve measurement problems.
Similar Triangles • The diagram shows a method for calculating the height of an object that is difficult to measure directly. • Place a mirror on a leveled spot at a convenient distance from the object. • Back up from the mirror until you see the reflection of the top of the object in the center of the mirror.
The two triangles in the diagram are similar. • To find the object’s height, you need to measure three distances and use similar triangles. • What distances do you think we should measure? Person’s height Object’s distance to mirror. Person’s distance to mirror.
What do you do next? • Once you have these three measurements, how do you find the height of the traffic light? • Set up a proportion and solve for the missing height. 160 cm 600 cm 200 cm
Set up and solve the proportion • Height of object = Height of personDistance of object to mirror Distance of person to mirror. • x = 160600 200 200x = 600(160) 200x = 96,000 x = 480 The height of the traffic light is 480 cm. 160 cm 600 cm 200 cm