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Indirect Measurement with Similar Triangles. Similar triangles can sometimes be used to measure unknown lengths or distances indirectly The lengths of corresponding sides of similar triangles are proportional
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Indirect Measurementwith Similar Triangles • Similar triangles can sometimes be used to measure unknown lengths or distances indirectly • The lengths of corresponding sides of similar triangles are proportional • Knowing the length of one pair of corresponding sides allows the lengths of the remaining sides to be found • In the picture at right the person is looking at the reflection of the flagpole in a mirror on the ground • Are the triangles in the picture similar? ∆EXP ~ ∆FXB • What pairs of sides are proportional? EX:FX XP:XB EP:FB • What pair of sides can both be measured? XP and XB • What additional measurement is needed to find the height of the flagpole? The distance EP from the eye to the ground
Indirect Measurementwith Similar Triangles • Another method of indirect measurement with similar triangles uses shadows • To use this method the rays of light must be parallel • Sunlight is one source of parallel rays of light • In the pictures below the shadows of the person and the lamppost are cast on the ground by the sun at the same time • Are the triangles in the picture similar? Yes, by AA • What pairs of sides are proportional? height, shadows • What is the ratio of the sides of the triangles? 1: 3 • What is the value of x, the height of the lamppost? 15.75 ft