dy/dt=e^t(cost+sint)
dx/dt=e^t(cost-sint)
所以dy/dx=(dy/dt)/(dx/dt)=(cost+sint)/(cost-sint)=1/)cos²t-sin²t)=1/cos2t=sec2t
d(dy/dx)/dt=(sec2t)'=2sec2t×tan2t
d²y/dx²=[d(dy/dx)/dt]/[dx/dt]=[2sec2t×tan2t]/[e^t(cost-sint)]