Proof problem: known: as shown in the figure, in the quadrilateral ABCD, ab ‖ CD, ab = CD. Proof: ad = CB
It is proved that: in △ abd and △ CDB, ab = CD ∠ abd = bdcbd = BD, ≌ abd ≌ △ CDB (SAS), ≌ ad = CB
It is proved that: in △ abd and △ CDB, ab = CD ∠ abd = bdcbd = BD, ≌ abd ≌ △ CDB (SAS), ≌ ad = CB