左边=cos(π-θ)/cosθ[sin(3π/2-θ)-1]+cos(2π-θ)/cos(π+θ)[sin(π/2+θ)-1]
=-cosθ/cosθ*[-cosθ-1]+cosθ/(-cosθ)*[cosθ-1]
=1/(cosθ+1)-1/(cosθ-1)
=1/(cosθ+1)+1/(1-cosθ)
=(1-cosθ+1-cosθ)/(1-cos^2θ)
=2/(1-cos^2θ)
=2/sin²θ
=右边
感觉原题有误,改之……
求证cos(π-θ)/cosθ[sin(3π/2-θ)-1]+cos(2π-θ)/cos(π+θ)sin(π/2+θ-s
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