设顶角为2θ
则cosθ=5/13,sinθ=12/13,tanθ=12/5
顶角的正弦 sin2θ=2tanθ/(1+tanθ²)=120/169
顶角的余弦 cos2θ=(1-tanθ²)/(1+tanθ²)=-119/169
顶角的正切 tan2θ=2tanθ/(1-tanθ²)=-120/119