Congruence and Similarity

Same shape, different size

• Two shapes are similar when one is an enlargement of the other, turned or flipped over if need be, which means their angles match and every pair of corresponding sides shares the same ratio
• Papers usually say "mathematically similar", occasionally just "similar", and either phrasing is the signal to look for a scale factor
• Congruence is the special case of similarity where the scale factor is 1, so congruent shapes are similar but similar shapes are usually not congruent