2sin2(α+β)是sin(α+β)的平方的2倍吧?tanα+tanβ=5,tanα*tanβ=6,tan(α+β)=(tanα+tanβ)/(1-tanα*tanβ)=-1.[sec(α+β)]^2=1+[tan(α+β)]^2=2,[cos(α+β)]^2=1/[sec(α+β)]^2=1/2.2[sin(α+β)]^2-3sin...