cos(theta) - tan(theta)*sec(theta)cos(θ)−tan(θ)⋅sec(θ)
=cos(theta) - sin(theta)/cos(theta) * 1/cos(theta)=cos(θ)−sin(θ)cos(θ)⋅1cos(θ)
=cos(theta) -sin(theta)/cos^2(theta)=cos(θ)−sin(θ)cos2(θ)
=sqrt(1-sin^2(theta)) - sin(theta)/(1-sin^2(theta))=√1−sin2(θ)−sin(θ)1−sin2(θ)
=((1-sin^2(theta))sqrt(1-sin^2(theta)) - sin(theta))/(1-sin^2(theta))=(1−sin2(θ))√1−sin2(θ)−sin(θ)1−sin2(θ)