4. (i)Obtuse vertically opposite angles means greater than 90 and equal ∠AOD = ∠BOC.
(ii) Adjacent complementary angles means angles have common vertex, common arm, non-common arms are on either side of common arm and sum of angles is 90° .
(iii) Equal supplementary angles means sum of angles is 180° and supplement angles are equal.
(iv) Unequal supplementary angles means sum of angles is 180° and supplement angles are unequal. i.e., ∠AOE, ∠EOC; ∠AOD, ∠DOC and ∠AOB, ∠BOC
(v) Adjacent angles that do not form a linear pair mean, angles have common ray but the angles in a linear pair are not supplementary. i.e., ∠AOB, ∠AOE; ∠AOE, ∠EOD and ∠EOD, ∠COD
