cos (θ-π/4)=-3/5,θ∈(π/2,π),tan θ=?
问题描述：
cos (θ-π/4)=-3/5,θ∈(π/2,π),tan θ=?
答
sin(θ-π/4)=4/5
tan(θ-π/4)=-4/3=(tanθ-tanπ/4)/(1+tanθtanπ/4)=(tanθ-1)/(1+tanθ)
tanθ=-7