Same angle.-same angle.

Above: ∠ 1=∠2, ∠ 1 and ∠ equiangular.

Below, ∠ 1 and ∠2 are complementary.

∠ 1 and∠ 3 are complementary,

Then ∠2 and ∠3 are the complementary angles of an angle (∠ 1).