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Similarity
Similar and congruent figures

Similar figures have equal corresponding angles and the length of their corresponding sides have equal ratios.

 Similar equlateral triangles Similar squares

Congruent figures have the same size as well as the same shape. They are similar figures that are equal in size.

 Congruent triangles Congruent squares Congruent rectangles Congruent Hexagons

Since $\frac{7}{10.5}=\frac{3}{4.5}=\frac{7}{10.5}=\frac{3}{4.5}$ , the measures of the sides of the polygons are proportional. The corresponding angles are congruent. Therefore, the polygons are similar.
Since $\frac{4}{3}=\frac{8}{6}=\frac{4}{3}=\frac{8}{6}$ , the measures of the sides of the polygons are proportional. However, the corresponding angles are not congruent. The polygons are not similar.