sinα+cosα=1/5,5sinα=1-5cosα ,25sin^2α=1-10cosα+25cos^2α
25cos^2α-5cosα-12=0 ,(5cosα+3)(5cosα-4)=0 ,cosα=-3/5或4/5 ,sinα=-3/5或4/5
要使sinα+cosα=1/5,必须cosα=-3/5 ,sinα=4/5
π/2
sinα+cosα=1/5,5sinα=1-5cosα ,25sin^2α=1-10cosα+25cos^2α
25cos^2α-5cosα-12=0 ,(5cosα+3)(5cosα-4)=0 ,cosα=-3/5或4/5 ,sinα=-3/5或4/5
要使sinα+cosα=1/5,必须cosα=-3/5 ,sinα=4/5
π/2