举报
88066348
∵tan(θ-π)=tanθ=-1/2 即sinθ/cosθ=-1/2 又∵sin²θ+cos²θ=1 解得sin²θ=1/5 cos²θ=4/5 (2)原式=sin²θ+3cos[kπ-(π/2+θ)]sin[kπ-(π/2-θ)]-1 =sin²θ+3coskπcos(π/2+θ)·[-coskπsin(π/2-θ)]-1 =sin²θ+3cos²kπ(-sinθ)(-cosθ)-1 =sin²θ+3tanθcos²θ-1 =1/5+3×(-1/2)×4/5-1 =1/5-6/5-1 =-2 (1)你再看看对不对 答案对不住啊。