看图片
dx/dt=2t/(1+t²)dy/dt=1- 1/(1+t²) =t²/(1+t²)故dy/dx=(dy/dt) / (dx/dt) =t/2d²y/dx²=[d(t/2)/dt] / (dx/dt)=1/2 · 2t/(1+t²)=(1+t²)/4t
