由lim(x趋于0)[f(x)+f(-x)]/x存在,得lim(x趋于0)[f(x)+f(-x)]=0.而f(x)在x=0处连续,得
lim(x趋于0)[f(x)+f(-x)]=lim(x趋于0)f(x)+lim(x趋于0)[f(-x)]=f(0)+f(0)=0.
故f(0)=0
由lim(x趋于0)[f(x)+f(-x)]/x存在,得lim(x趋于0)[f(x)+f(-x)]=0.而f(x)在x=0处连续,得
lim(x趋于0)[f(x)+f(-x)]=lim(x趋于0)f(x)+lim(x趋于0)[f(-x)]=f(0)+f(0)=0.
故f(0)=0