诚心求教数学,希望帮帮忙~~1.已知α、β属于(3π/4,π),sin(α+β)=-3/5,sin(β-π/4)=12/13,则cos(α+π/4)等于()A.16/65 B.56/65 C.-16/65 D.56/652.已知α,β属于(0,π),tan(α-β)=1/2,tanβ=-1
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![诚心求教数学,希望帮帮忙~~1.已知α、β属于(3π/4,π),sin(α+β)=-3/5,sin(β-π/4)=12/13,则cos(α+π/4)等于()A.16/65 B.56/65 C.-16/65 D.56/652.已知α,β属于(0,π),tan(α-β)=1/2,tanβ=-1](/uploads/image/z/14707743-15-3.jpg?t=%E8%AF%9A%E5%BF%83%E6%B1%82%E6%95%99%E6%95%B0%E5%AD%A6%2C%E5%B8%8C%E6%9C%9B%E5%B8%AE%E5%B8%AE%E5%BF%99%7E%7E1.%E5%B7%B2%E7%9F%A5%CE%B1%E3%80%81%CE%B2%E5%B1%9E%E4%BA%8E%EF%BC%883%CF%80%2F4%2C%CF%80%EF%BC%89%2Csin%EF%BC%88%CE%B1%EF%BC%8B%CE%B2%EF%BC%89%3D%EF%BC%8D3%2F5%2Csin%28%CE%B2-%CF%80%2F4%29%3D12%2F13%2C%E5%88%99cos%EF%BC%88%CE%B1%2B%CF%80%2F4%EF%BC%89%E7%AD%89%E4%BA%8E%EF%BC%88%EF%BC%89A.16%2F65++++B.56%2F65++++++C.%EF%BC%8D16%2F65++++D.56%2F652.%E5%B7%B2%E7%9F%A5%CE%B1%2C%CE%B2%E5%B1%9E%E4%BA%8E%EF%BC%880%2C%CF%80%EF%BC%89%2Ctan%EF%BC%88%CE%B1-%CE%B2%EF%BC%89%3D1%2F2%2Ctan%CE%B2%3D%EF%BC%8D1)
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