Bisectors of the angles B and C of an isosceles triangle ΔABC with AB = AC intersect each other at O. BO is produced to a point M.
In ΔABC, we have
∴∠ABC=∠ACB [ ∵ Angles opposite to equal sides of a triangle are equal.]
∠MOC=∠1+∠2 [ ∵ Exterior angle of a triangle is equal to the sum of interior opposite angles]
[ ∵ ∠1=12∠ABC ]