已知cos(75°+θ)=1/3,θ为第三象限角,求cos(-225°-θ)+sin(435°+θ)的值.·······若有大神路_数学解答

已知cos(75°+θ)=1/3,θ为第三象限角,求cos(-225°-θ)+sin(435°+θ)的值.
·······若有大神路过,顺便帮个忙~
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人气：348 ℃　时间：2020-02-06 05:47:06

解答

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...