x=g(t)y=h(t)则一阶导数：dy/dx=h'(t)/g'(t)二阶导数：d²y/dx²=d[h'(t)/g'(t)]/dx 函数中只有变量t,t看作中是变量={d[h'(t)/g'(t)]/dt}*(dt/dx)={d[h'(t)/g'(t)]/dt} / (dx/dt)={d[h'(t)/g'(t)]/dt} / g'(...