已知cos(75+θ)=1/3,θ为第三象限角,求cos(-255-θ)+sin(435+θ)的值.
问题描述:
已知cos(75+θ)=1/3,θ为第三象限角,求cos(-255-θ)+sin(435+θ)的值.
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答
cos(-255°-θ)+sin(435°+θ)=cos(255°+θ)+sin(360°+75°+θ) =cos(180°+75°+θ)+sin(75°+θ) =-cos(75°+θ)+sin(75°+θ) θ为第三象限角,75°+θ为第三或第四象限角 sin(75°+θ)=-根号下(1-cos^2[(75°+...