In the below quadrilateral ABCD, if AD = BC and ∠DAB = ∠CBA, then what is the relation between ∠ABD and ∠BAC ?
∠ABD = ∠BAC
In ΔABD and ΔBAC,
AD = BC (Given)
∠BAD = ∠CBA (Given)
AB = BA (Side common to both triangles)
Hence ΔABD≅ΔBAC
(by SAS congruence condition).
Thus, ∠ABD = ∠BAC
(corresponding parts of congruent triangles).