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20 10 Foshan One Model Math Problem (PS: Junior High School)
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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