(1)∵θ∈(π/2,π)∴tanθ<0tanθ=-2/3tan(θ-π/4)=(tanθ-tanπ/4)/(1-tanθtanπ/4)=(-2/3-1)/[1-(-2/3)*1]=(-5/3)/(5/3)=-1(2) 原式=[2sinθcosθ]/[sin^2θ-3sin^2θ]=-cosθ/sinθ=-1/tanθ=-1/(-2/3)=3/2
