>_>_
>_因为x^2-6xsinθ+tanθ=0两根相等所以Δ=36sin^2θ-4tanθ=0得2sinθcosθ=2/9(sinθ+cosθ)^2=sin^2θ+2sinθcosθ+cos^2θ=1+2/9=11/9所以sinθ+cosθ=√(11/9)