y=2e^2x
y'=2e^2x*(2x)'=4*e^2x
dy/dt=2t*e^t+t²e^t=(t²+2t)*e^t
d²y/dt²=(2t+2)e^t+(t²+2t)e^t=(t²+4t+2)e^t
dx/dt=(t+1)e^t
d²x/dt²=(t+2)*e^t
所以d²y/dx²=(d²y/dt²)/(d²x/dt²)=(t²+4t+2)/(t+2)