The SAS (Side-Angle-Side) criterion for triangle similarity states that if two triangles have one angle that is included between two pairs of proportional sides, then the triangles are similar.
In other words, if you have two triangles \(ABC\) and \(DEF\), and you can show that:
- The lengths of two sides of triangle \(ABC\) are proportional to the lengths of the corresponding sides of triangle \(DEF\) (i.e., \(\frac{AB}{DE} = \frac{AC}{DF}\)), and
- The angle between those two sides in triangle \(ABC\) is equal to the angle between the corresponding sides in triangle \(DEF\) (i.e., \(\angle A = \angle D\)),
then it can be concluded that triangle \(ABC\) is similar to triangle \(DEF\) (denoted as \(ABC \sim DEF\)). This means that their corresponding angles are equal, and their corresponding side lengths are in proportion.
So, in summary, if the two sides of each triangle are proportional and the included angle is the same, then the triangles themselves are similar according to the SAS criterion.