## Thinking Mathematically (6th Edition)

$\triangle{I} \cong \triangle{II}$ by SAS postulate
The triangles share a common side so that side counts as one pair of congruent sides. The two triangles have another pair of congruent corresponding sides (as labeled in the figure). The angles included by these two sides are both 90-degrees, so they are congruent. Thus, by the SAS postulate, $\triangle{I} \cong \triangle{II}$.