1. **State the problem:** Determine if the two triangles described in the first graph (top-left) are congruent and explain why. 2. **Description:** Two triangles share a base with a vertical line from the top vertex perpendicular to the base. Both sides adjacent to the vertical line have equal marks, and there is a right angle at the base. 3. **Relevant congruence criteria:** Triangles are congruent if they satisfy any of the following: Side-Side-Side (SSS), Side-Angle-Side (SAS), Angle-Side-Angle (ASA), Angle-Angle-Side (AAS), or Right angle-Hypotenuse-Side (RHS) for right triangles. 4. **Apply the RHS criterion:** Since the vertical line is perpendicular to the base, it forms a right angle in both triangles. 5. Both triangles share the base (common side). 6. The two sides adjacent to the vertical line are marked equal. 7. Therefore, the triangles have a right angle, a hypotenuse (the base), and one side equal. 8. By the RHS (Right angle-Hypotenuse-Side) criterion, the two triangles are congruent. 9. **Final answer:** The two triangles are congruent by the RHS criterion because they have a right angle, a common hypotenuse, and one pair of equal sides adjacent to the right angle.