因为cos2a=1-2sin^2a由题知,(1-cos2a)/(sinacosa)=1所以,2sin^2a / (sinacosa)=1所以,sina / cosa = 1/2即tana=1/2因为tana=1/2,tan(a-b)=-2/3所以,tan(b-2a)=-tan(2a-b)=-[tana+tan(a-b)] / [1-tana*tan(a-b)]=-[(1...