α,β∈(0,π/2),cos(α+β)=5/13,sin(α-β)=-4/5,则cos2α=?
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α,β∈(0,π/2),cos(α+β)=5/13,sin(α-β)=-4/5,则cos2α=?
α,β∈(0,π/2),cos(α+β)=5/13,sin(α-β)=-4/5,则cos2α=?
α,β∈(0,π/2),cos(α+β)=5/13,sin(α-β)=-4/5,则cos2α=?
由α,β∈(0,π/2),cos(α+β)=5/13>0,知α+β∈(0,π/2),则sin(α+β)=12/13
又sin(α-β)=-4/5
上面那位的回答是对的那