数学题三角函数已知2sin(3π+θ)=cos(π+θ),求2sin^2 θ+3sinθcosθ-cos^2 θ

2sin(3π+θ)=cos(π+θ)2sinθ=cosθtanθ=1/22sin^2 θ+3sinθcosθ-cos^2 θ 2sin^2 θ+3sinθcosθ-cos^2 θ ___________________________= ____________________________= 1 sin^2 θ +cos^2 θ分子分母同除以cos^2 θ 2tan^2θ+3tanθ-1________________ 将tanθ=1/2带入tan^2θ+1 =4/5