Big Ideas Math: Modeling Real Life, Grade 8
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4. Using Similar Triangles
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Exercise 5 Page 125

Similar figures have the same shape but not necessarily the same size. Recall that a similarity transformation is a dilation or a sequence of dilations and rigid motions.

Which Is Different? Are △ PQR and △ TSR the same size and shape?
Answers: See solution.

Practice makes perfect

We want to determine which of the given questions is different. Let's read them!

First, let's recall that a dilation is a type of transformation in which a figure is made smaller or larger with respect to a point called the center of dilation. Notice that a scale drawing is an example of a dilation. This means that two out of the four questions ask about the same thing.

Next, let's recall that a similarity transformation is a dilation or a sequence of dilations and rigid motions. Therefore, if two figures are similar, then one of them is a dilation or a scale drawing of the other one.

This means that the only question that is different is whether △ PQR and △ TSR are the same size and shape. Now, let's take a look at the given diagram.

We can see that △ PQR and △ TSR are the same shape but they are not the same size. Next, sides TS and PQ are parallel and both are intersected by side RQ. Therefore, ∠ TSR and ∠ PQR are congruent, corresponding angles.

Additionally, both triangles share ∠ R. This means that two angles in △ PQR are congruent to two angles in △ TSR, so the third angles are also congruent. Therefore, △ PQR and △ TSR are similar. We can also say that △ PQR is a dilation or a scale drawing of △ TSR.