The two angles of ΔABC are equal to the two respective angles of ΔFED. Also, the sum of all interior angles of a triangle is 180º. Therefore, third angle of both triangles will also be equal in measure.
Both triangles have right angles. Also the the two dashes on BC and DE indicate that those 2 sides of the triangles are the same. Angle A and angle F are also the same. This is what makes the triangles congruent
