Congruence and similarity

Congruent shapes: shapes which are identical and are the same size. This is even true if the shapes have been rotated or reflected. The shapes below are congruent.

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When two shapes are the same but different sizes, they are said to be similar. The triangles below are said to be similar.

To find a length of a similar shape, you want to find out what the scale factor is (how much bigger is the larger shape). Then multiply the length you do know, by the scale factor.