∵sinθ+cosθ=1/5.(1)∴(sinθ+cosθ)²=1/25∴sinθcosθ=-12/250,∴cosθ0∵(sinθ-cosθ)²=1-2sinθcosθ=49/25,∴sinθ-cosθ=7/5.(2)∴由(1)(2)得sinθ=4/5,cosθ=-3/5.故tanθ=sinθ/cosθ=-4/3....