In Fig. 10.16, OAB = 30º and OCB = 57º. Find BOC and AOC.
AOC = 54° and BOC = 66°
Solution:
Given: OAB = 30°, OCB = 57°C
In OAB,
AO = BO (radius of the same circle)
OAB = OBA = 30° (Angles opposite to equal sides are equal)
In AOB, the sum of all angles is 180°.
OAB + OBA + AOB = 180°.
30° + 30° + AOB = 180°
AOB = 180° – 30° – 30°
AOB = 120° … (i)
Now, in OBC,
OC = OB (radius of the same circle)
OBC = OCB = 57° (Angles Opposite to equal sides are equal).
In OBC, the sum of all angles is 180°.
OBC + OCB + BOC = 180°
57° + 57° + BOC = 180°
BOC = 180° – 57° – 57°
BOC = 66° … (ii)
Now, form equation (i) we have
AOB = 120°.
AOC + COB = 120°
AOC + 66° = 120° (from ii)
AOC = 120° – 66°
AOC = 54° and BOC = 66°.