sinθ-2cosθ=0sinθ=2cosθ∴ sin2θ+sinθcosθ-2cos2θ=(sin²θ+sinθcosθ-2cos²θ)/(sin²θ+cos²θ)=(4cos²θ+2cos²θ-2cos²θ)/(4cos²θ+cos²θ)=4cos²θ/...