In the triangles unit you learned about congruent triangles and the minimum number of congruent sides and/or angles needed in order to verify that the triangles were congruent.  Those theorems were named SSS, SAS, etc.  Some of these special relationships can also be used to determine when two triangles are similar.  These triangle similarity relationships will resemble the triangle congruence statements.  Like any shape, in order for two triangles to be similar, the corresponding angles must be congruent and the corresponding sides must have the same ratio.   Because the similarity and congruence statements are so much alike, it is very important to use the congruence or similarity symbols when comparing two triangles.

Congruent figures have the same shape and size.  Similar figures have the same shape, but not necessarily the same size.  Therefore, congruent figures are always similar but similar figures are not always congruent.

The rest of this unit will discuss similarity of triangles.  For an interactive to help understand the relationship between similar triangles, select the following link:

Similar Triangles