Label the angles on the given figure an x and y and label the unknown angles as z (see the figure below).
Because the sum of angles in a triangle = 180°, angle z is correct for all three triangles.
In order to prove that ΔINF = ΔCAT by the ASA Postulate,
1. We should show that AC = IN, or
2. We should show that AT = NF.
Proving either of the two options means that we have congruent isosceles triangles.
