The angle-angle-side (AAS) theorem is used to determine when two triangles are congruent. By the theorem, two triangles are congruent if they have two angles of equal measure and one side adjacent to only one of the angles that are equal in length. Explanation:
In △ABC & △DEF ∠F=∠A(40∘) ∠B=∠E(90∘) BC=DE( Equal in Length ) ∴∠ABC≅∠FED (by Angle - Angle - Side Property)