x^2/a^2-y^2/b^2=x^2/x^2(cosθ)^2-b^2(tanθ)^2/b^2=1/(cosθ)^2-(tanθ)^2=1/(cosθ)^2-(sinθ)^2/(cosθ)^2=[1-(sinθ)^2]/(cosθ)^2=(cosθ)^2/(cosθ)^2=1
