Which of the following are necessary when proving that the diagonals of a rectangle are congruent check all that apply

If you take the rectangle with the geometric center O. Match the sides of  opposite triangles. AB will be equal to CD and AC is equal to BD. Angles AOB is equal to the angle COD and angle AOC is equal to angle BOD.

The two diagonals bisect each other and therefore each all parts of the diagonal are equal.

Therefore the two diagonals are congruent.

m∠a is 90°

m∠b is 40°