利用狄利克雷函数D(x):
1 ,当x是有理数时;
D(x) = .
0 ,当x是无理数时.
可以定义:
x^2 ,当x是有理数时;
f(x) = x^2*D(x)= .
0 ,当x是无理数时.
则:
① f(x)在 x≠0 时,极限不存在,不连续,不可微.
② f(x)在 x =0 时,连续,可导,可微:
f'(0) = lim(x->0) [f(x) - f(0)]/x = lim(x->0) f(x)/x = 0
利用狄利克雷函数D(x):
1 ,当x是有理数时;
D(x) = .
0 ,当x是无理数时.
可以定义:
x^2 ,当x是有理数时;
f(x) = x^2*D(x)= .
0 ,当x是无理数时.
则:
① f(x)在 x≠0 时,极限不存在,不连续,不可微.
② f(x)在 x =0 时,连续,可导,可微:
f'(0) = lim(x->0) [f(x) - f(0)]/x = lim(x->0) f(x)/x = 0