求值已知sinθ+cosθ=
已知sinθ+cθ=-√10/5。求1/sinθ+1/cosθ的值，tanθ的值
sinθ+cosθ=-√10/5 （sinθ+cosθ）^2=（-√10/5）^2 1+sin2θ=2/5 sin2θ=-3/5 1/sinθ+1/cosθ =2(sinθ+cosθ)/sin2θ =√10/3 sin2θ=2tanθ/(1+tan^θ) 2tanθ/(1+tan^θ)=-3/5 3tan^θ+10tanθ+3=0 tanθ=-3,tanθ=-1/3