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已知0已知0已知0sin(ab)=12/13sin(a-b)=-4/5cos2b=cos[(ab)-(a-b)]=cos(ab)cos(a-b)sin(ab)sin(a-b)=-15/65-48/65

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sin(a b)=12/13
sin(a-b)=-4/5
cos2b=cos[(a b)-(a-b)]=cos(a b)cos(a-b) sin(a b)sin(a-b)=-15/65-48/65=-63/65