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Having the same shape but not necessarily the same size (see congruent). Two triangles are similar if they have equal angles and their corresponding sides, say, a1, b1, c1 and a2, b2, c2, have a common ratio, r : a1/a2 = b1/b2 = c1/c2. In general, a similarity is a transformation under which the distance between any corresponding pair of points changes by the same factor.

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