已知sin(θ＋kπ)=2cos[θ＋（k+1）π],k∈Ζ,求4sinθ-2cosθ/5cosθ+3sinθ的值

题目

已知sin(θ＋kπ)=2cos[θ＋（k+1）π],k∈Ζ,求4sinθ-2cosθ/5cosθ+3sinθ的值

答案

sin(θ+kπ)=2cos[θ+(k+1)π]
=-2cos(θ+kπ)
tan(θ+kπ)=sin(θ+kπ)/(-2cos(θ+kπ))=-1/2
tanθ=-1/2
4sinθ-2cosθ/5cosθ+3sinθ=(4tanθ-2)/(5+3tanθ)
=-8/7