? ∴BC=80/tan27

2. Connect PQ, cross AD at point R, cross BC at point H, and connect DQ.

? Let the side length of a square be 2a, then Dr = ch = a, QH = √ 3a, and RH = 2a.

∴RQ=(2+√3)a

? In Rt△DRQ, tan∠PQD=DR/RQ=a/(2+√3)a=2-√3.

3. Make CE⊥AB at point E,

? In Rt△ACE, there is tan∠ACE=AE/CE.

AE=btanα

? ∴AB=btanα+a