if angle 1 is complementary to angle 2 then m angle 1 + m angle 2 = 90given AC = 12 and B is between A and C then AB + BC = 12If angle A and angle B form a linear pair, then angle A and angle B are supplementary

If angle 1 is complementary to angle 2, then m∠1 + m∠2 = 90.
This statement is the Definition of Complementary Angles. The sum of complementary angles is 90 degrees.
Complementary angles always come in pairs while right angle is just one.