作业帮cos2a/sin(a-pai/4)=-根号2／2求cosa＋sina
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cos2a/sin(a-pai/4)=-根号2／2求cosa＋sina
cos2a/sin(a-pai/4)=-根号2／2
cos2a/(sinacos(pai/4)-cosasin(pai/4))=-根号2／2
cos2a/(根号2／2*sina-根号2／2*cosa)=-根号2／2
cos2a/根号2／2*(sina-cosa)=-根号2／2
(cos^2 a-sin^2 a)/(sina-cosa)=-1/2
(cosa-sina)(cosa+sina)/(sina-cosa)=-1/2
cosa+sina=1/2.
cos2a/(sinacos(pai/4)-cosasin(pai/4))=-根号2／2
cos2a/(根号2／2*sina-根号2／2*cosa)=-根号2／2
cos2a/根号2／2*(sina-cosa)=-根号2／2
(cos^2 a-sin^2 a)/(sina-cosa)=-1/2
(cosa-sina)(cosa+sina)/(sina-cosa)=-1/2
cosa+sina=1/2.
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