f（x）=sin（x+θ）+sin（x-θ）-2sinθ=2[sin(x+θ+x-θ)/2*cos(x+θ-x+θ)/2]-2sinθ=2sinx*cosθ-2sinθ=√(4sin^2x+4)cos(α+θ)≥0θ∈(0,π/2)tan2θ=-3/42θ∈(π/2,π)sin2θ=-3/4cos2...