## Elementary Geometry for College Students (6th Edition)

Each of two right triangles has an angle of $90^{\circ}$. Therefore, for any of two right triangles, they already have a congruent pair of $90^{\circ}$ angles. Therefore, if two right triangles $\triangle A$ and $\triangle B$ also have congruent pairs of legs, they now have 2 congruent sides and a congruent included angle, which is the congruent pair of $90^{\circ}$ angles. So, these two right triangles would be congruent with each other according to postuale SAS. In conclusion, LL is just a special case of postulate SAS.