f'(0)
=lim(x→0) [f(x)-f(0)]/x 替换x为-t
=lim(t→0) [f(-t)-f(0)]/(-t)
=lim(t→0) [f(t)-f(0)]/(-t)
=-lim(t→0) [f(t)-f(0)]/t
=-f'(0)
所以,f'(0)=0
f'(0)
=lim(x→0) [f(x)-f(0)]/x 替换x为-t
=lim(t→0) [f(-t)-f(0)]/(-t)
=lim(t→0) [f(t)-f(0)]/(-t)
=-lim(t→0) [f(t)-f(0)]/t
=-f'(0)
所以,f'(0)=0