sin(a-b)cosa-cos(a-b)sina=3/5 求sinbb为第三象限角

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sin(a-b)cosa-cos(a-b)sina=3/5 求sinbb为第三象限角
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sin(a-b)cosa-cos(a-b)sina=3/5 求sinbb为第三象限角
sin(a-b)cosa-cos(a-b)sina=3/5 求sinb
b为第三象限角

sin(a-b)cosa-cos(a-b)sina=3/5 求sinbb为第三象限角
根据公式sin(a-b)=sinacosb-cosasinb
sin(a-b)cosa-cos(a-b)sina 把（a-b）看成一项 逆着用上边的公式 有
sin(a-b)cosa-cos(a-b)sina =sin(a-b-a)
=sin(-b)
=-sinb=3/5
所以sinb=-3/5

sin(a-b)cosa-cos(a-b)sina=sin((a-b)-a)=sin(-b)=-sinb=3/5
sinb=-3/5

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