Judging from the meaning of the question, ∠DAB=α, ∠ dad' = β;
∵△ABC?△BAD '
∴∠ Dabu = ∠ ABC; That is, α+β = ∠ ABC; ( 1)
∵ Quadrilateral ABCD is a parallelogram (or AD//BC).
∴ ∠ABC+∠DAB= 180? (2)
Substitute (1) into (2) to get α+β+α= 180?
∴β= 180? -2α