由sinβ+cosβ=1/5,可知 （sinβ+cosβ）²=1/25,解得sin2β=-24/25,则3π/2>2β>5π/4,3π/4>β>5π/8.由sin2β²+cos2β²=1,得cos2β=-7/25,∴tan2β=24/7,解得tanβ=-4/3设sinβ—cosβ=t ① ①+②...