Step-by-step explanation:
complementary angles mean together they have 90°.
2 angles are congruent, when they have the same size.
so, we can actually translate the given situation into
A + C = 90°
B + D = 90°
A = B
therefore, we can rewrite the first 2 equations as
A + C = 90°
A + D = 90°
C = 90 - A
D = 90 - A
therefore, C = D, and therefore C and D are congruent.
