You know the meaning of the word similar in everyday speech. In geometry, it has a related but more technical meaning. Two figures are similar if they have exactly the same shape.
Similar Figures
In this section, I cover the formal definition of similarity, how similar figures are named, and how they’re positioned.
Defining similar polygons
As you see in Figure 8-1, quadrilateral WXYZ is the same shape as quadrilateral ABCD, but it’s ten times larger (though not drawn to scale). These quadrilaterals are therefore similar.
Similar polygons: For two polygons to be similar, both of the following must be true:
Corresponding angles are congruent.
Corresponding sides are proportional.
FIGURE 8-1: These quadrilaterals are similar because they’re exactly the same shape; note that their angles are congruent.
To fully understand this definition, you ...
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Sizing up similar figures
Similar polygons: For two polygons to be similar, both of the following must be true: