已知cos(75°+θ)=1/3,θ为第三象限角,求cos(255°+θ)+sin(435°+θ)
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![已知cos(75°+θ)=1/3,θ为第三象限角,求cos(255°+θ)+sin(435°+θ)](/uploads/image/z/1730070-54-0.jpg?t=%E5%B7%B2%E7%9F%A5cos%2875%C2%B0%2B%CE%B8%29%3D1%2F3%2C%CE%B8%E4%B8%BA%E7%AC%AC%E4%B8%89%E8%B1%A1%E9%99%90%E8%A7%92%2C%E6%B1%82cos%28255%C2%B0%2B%CE%B8%29%2Bsin%28435%C2%B0%2B%CE%B8%29)
已知cos(75°+θ)=1/3,θ为第三象限角,求cos(255°+θ)+sin(435°+θ)
已知cos(75°+θ)=1/3,θ为第三象限角,求cos(255°+θ)+sin(435°+θ)
已知cos(75°+θ)=1/3,θ为第三象限角,求cos(255°+θ)+sin(435°+θ)
cos(255°+θ)+sin(435°+θ)
=cos(75°+180°+θ)+sin(75°+360°+θ)
=sin(75°+θ)-cos(75°+θ)
θ为第三象限角
cos(75°+θ)=1/3>0
∴75°+θ是第四象限角
∴sin(75°+θ)
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