sinα+cosα除以sinα-cosα等于2sinα+cosα=2(sinα-cosα)sinα+cosα=2sinα-2cosαsinα=3cosαsin^2α=(3cosα)^2sin^2α=9cos^2αsin^2α=9(1-sin^2α)sin^2α=9-9sin^2αsin^2α=9/10