"tan^2θ"表示θ的正切值(tanθ)的平方，具體可以表示為：tan^2θ = (tanθ)^2= (sinθ/cosθ)^2= sin^2θ/cos^2θ= sin^2θ/(1-sin^2θ)= (1-cos^2θ)/cos^2θ