若cos2α/sin(α-π/4)=-根2/2,则cosα+sinα的值为?
问题描述:
若cos2α/sin(α-π/4)=-根2/2,则cosα+sinα的值为?
答
亲爱的楼主:
cos2α/sin(α-π/4)=-√2/2(cos^2α-sin^2α)/(sinαcosπ/4-cosαsinπ/4) = -√2/2[(cosα+sinα)(cosα-sinα)] / [√2/2(sinα-cosα)] = -√2/2-√2(cosα+sinα)(cosα-sinα) / (cosα-sinα) = -√2/2-√2(cosα+sinα) = -√2/2cosα+sinα = 1/2
祝您步步高升