sinα+cosβ=3/5 …①cosα+sinβ=4/5 ...②①²+②²,2+2(sinαcosβ+cosαsinβ)=1 ∴sin(α+β)= -1/2.①²-②²,cos2α-cos2β+2(cosαsinβ-sinαcosβ)=7/25 ∴-2sin(α+β)sin(α-β)-2sin(...