In the quadrilateral ABCD, if AD = BC and ∠DAB = ∠CBA, then relation between ∠ABD and ∠BAC is
∠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).
∴ ∠ABD = ∠BAC (congruent parts of congruent triangles).