In the given figure, 
is an isosceles triangle in which 
and a circle passing through 
and 
intersects 
and 
at 
and 
respectively.
Prove that 
Given AB = AC
∴ ∠ACB = ∠ABC
Ext. ∠ADE = ∠ACB = ∠ABC
∴ ∠ADE = ∠ABC
∴ DE || BC Proved.
17
In the given figure, is an isosceles triangle in which and a circle passing through and intersects and at and respectively.
Prove that
Given AB = AC
∴ ∠ACB = ∠ABC
Ext. ∠ADE = ∠ACB = ∠ABC
∴ ∠ADE = ∠ABC
∴ DE || BC Proved.