cos2α/sin(α-π/4)=(cosα平方-sinα平方)/(根号2/2sinα-根号2/2cosα)=-根号2(cosα+sinα)=-根号2/2
所以cosα+sinα=1/2
cos2α/sin(α-π/4)=-根号2/2,则cosα+sinπα等于什么
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