Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
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Exercise 1 Page 453

By similarity properties, the shortest and longest sides of two similar triangles correspond to each other.

See solution.

Practice makes perfect

We were given a triangle XYZ.

Let's suppose that △ ABC is similar to △ XYZ. Notice that by similarity properties the shortest sides of two similar triangles correspond to each other. Similarly, the longest sides also correspond to each other.
Side of △ XYZ Corresponds to
Shortest side of △ XYZ (10) Shortest side of △ ABC (l_1)
Longest side of △ XYZ (13) Longest side of △ ABC (l_2)
Third side of △ XYZ (12) Third side of △ ABC (l_3)

We have three ways to find the scale factor.

  1. If we are given the shortest side of △ ABC, the scale factor is k = l_110.
  2. If we are given the longest side of △ ABC, the scale factor is k = l_213.
  3. If we are given the third side of △ ABC, the scale factor is k = l_312.

On the other hand, if we are given one side of △ ABC — let's say AB — but we are not told which side is (l_1, l_2, or l_3), then we will not know which correspondence to use and we can get an incorrect scale factor. k_1 = AB/10 or k_2 = AB/13 or k_3 =AB/12 That is why we needed to know which side is 20 units long — so that we found the correct corresponding scale factor and then the length of the other two sides.