已知cos(75°+θ)=1/3,θ为第三象限角,求cos(-225°-θ)+sin(435°+θ)的值.

题目

已知cos(75°+θ)=1/3,θ为第三象限角,求cos(-225°-θ)+sin(435°+θ)的值.
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答案

cos(75°+θ)=1/3,θ为第三象限角设 75°+θ=A∴ θ=A-75°则 cosA=1/3, A是第四象限角∴ sinA=-√(1-cos²A)=-2√2/3 cos(-225°-θ)+sin(435°+θ)=cos(225°+θ)+sin(435°+θ)=cos(225°+A-75°)+sin(435...