From the figure,
(a) ∠AOD is a/an right angle.
Is anyone angle in the triangle is equal to 90o then the triangle is called right triangle.
∠AOD = ∠AOB + ∠BOC + ∠COD
= 30o + 20o + 40o
= 90o
(b) ∠COA is a/an acute angle
An acute angle is an angle formed between 0o to 90o.
∠COA = ∠COB + ∠BOA
= 20° + 30°
= 50o
(c) ∠AOE is a/an obtuse angle
An obtuse angle is an angle formed between 90o to 180o.
∠AOE = ∠EOD + ∠DOC + ∠COB + ∠BOA
= 40° + 40° + 20° + 30°
= 130°