求y对x的二阶导？x=f'(t).y=tf'(t)-f(t)那么一阶导y'/x'=（tf''(t)+f'(t)-f'(t)）/f''(t)=t二阶导=t'/x'=1/f''(t)就是等于f(t)的二阶导的倒数。希望对你有帮助O(∩_∩)O~
