sin(θ-45°)=12/13,135°

来源：学生作业帮助网编辑：作业帮时间：2024/11/30 09:52:12

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sin(θ-45°)=12/13,135°
sin(θ-45°)=12/13,135°<θ<225°,求cosθ的值提示：θ=（θ-45°）+45°

sin(θ-45°)=12/13,135°
cos(a)=cos((a-45)+45)=cos(a-45)*cos45-sin(a-45)*sin45
135

cosa=cos[(a-45)+45]=cos(a-45)cos45-sin(a-45)sin45=[cos(a-45)-sin(a-45)]*(#2/2),#指开根号
90cos(a-45)=-#{1-[sin(a-45)]^2}=-5/13
cosa=（-17/13)*(#2/2)

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