∵β∈(2/π,π)∴sinβ=√(1-cos^2 β) = 8/13;∵α∈(0,2/π),β∈(2/π,π)∴α+β∈(2/π,2/3π),∴cos(α+β)=-√[1-sin^2 (α+β)] = -56/65则sinα=sin[(α+β)-β]=sin(α+β)·cosβ-cos(α+β)·sinβ=283...