In Fig. 8.44, ∠AOF and ∠FOG form a linear pair.
∠EOB = ∠FOC = 90° and ∠DOC = ∠FOG = ∠AOB = 30°
(i) Find the measures of ∠FOE, ∠COB and ∠DOE.
(ii) Name all the right angles.
(iii) Name three pairs of adjacent complementary angles.
(iv) Name three pairs of adjacent supplementary angles.
(v) Name three pairs of adjacent angles.
(i) Say,
∠FOE = x
∠DOE = y
∠BOC = z
∠AOF + 30o = 180o (∠AOF + ∠FOG = 180o)
∠AOF = 150o
∠AOB + ∠BOC + ∠COD + ∠DOE + ∠EOF = 150o
30o + z + 30o + y + x = 150o
x + y + z = 90o(i)
Now,
∠FOC = 90o
∠FOE + ∠EOD + ∠DOC = 90o
x + y + 30o = 90o
x + y = 60o (ii)
Using (ii) in (i), we get
x + y + z = 90o
60o + z = 90o
z = 30o (∠BOC = 30o)
∠BOE = 90o
∠BOC + ∠COD + ∠DOE = 90o
30o + 30o + ∠DOE = 90o
∠DOE = 30o
Now, we have
x + y = 60o
y = 30o
∠FOE = 30o
(ii) Right angles are:
∠DOG, ∠COF, ∠BOF, ∠AOD
(iii) Three pairs of adjacent complimentary angles are:
∠AOB, ∠BOD
∠AOC, ∠COD
∠BOC, ∠COE
(iv) Three pairs of adjacent supplementary angles are:
∠AOB, ∠BOG
∠AOC, ∠COG
∠AOD, ∠DOG
(v) Three pairs of adjacent angles are:
∠BOC, ∠COD
∠COD, ∠DOE
∠DOE, ∠EOF