sinα+cosα=1/5(sinα+cosα)^2 = (sinα)^2 +(cosα)^2 +sin2α =1 +sin2α =1/25sin2α = -24/25 (1)cos2α = (1-(24/25)^2)^0.5 = -7/25(2)tan[2α-(π／4)]= （sin2αcos(π／4) -cos2αsin(π／4)）/(cos2αco...