sinθ+cosθ=1/5,sin²θ+cos²θ=1 , θ∈(0,π), sinθ>0将cosθ=1/5-sinθ代入sin²θ+cos²θ=1,得sin²θ-1/5sinθ-12/5=0(sinθ-4/5)*(sinθ+3/5)=0sinθ=4/5,cosθ=-3/5tanθ=sinθ/cosθ=-4/3sinθ-cosθ=4/5-(-3/5)=7/5sin³θ=(4/5)³=64/125cos³θ=(-3/5)³=-27/125