In Fig.10.13, ADC = 130° and chord BC = chord BE. Find CBE.
100°
Solution:
Consider BCO and BEO
BC = BE as given.
BCO = BEO (angles opposite to equal sides in a triangle are equal)
BO = BO (common sides)
BCO BEO (SAS congruence)
CBO = OBE (CPCT) …(i)
Now we know that ABCD is a Cyclic quadrilateral,
So, ADC + ABC = 180°
130° + ABC = 180°
ABC = 180°-130° = 50°
OBE = 50°
From (i)
CBO =OBE = 50°
CBE = CBO + OBE = 50° + 50° = 100°.