Sum of angles of linear pair is 180°.
(a) If one angle is acute angle, then other angle will be obtuse. As, if we subtract an acute angle from 180°, we get an angle which is greater than 90°.
(b) If one angle is obtuse angle, then other angle will be acute. As, if we subtract an obtuse angle from 180°, we get an angle which is less than 90°.
(c) If one angle is right angle, then other angle will also be right angle. As, if we subtract 90° from 180°, we get 90°.