1/cosθ -1/sinθ=1(sinθ-cosθ)/(sinθcosθ)=1sinθ-cosθ=sinθcosθ(sinθ-cosθ)²=(sinθcosθ)²sin²θ+cos²θ-2sinθcosθ=(sinθcosθ)²1-2sinθcosθ=(1/4)(2sinθcosθ)²1-...