魏尔斯特拉斯函数为什么处处不可导?

mathematica

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\[f(x) = \sum\limits_{n = 0}^\infty  {{a^n}\cos ({b^n}\pi x)} \]
这个函数的每一项都是可导的,为什么无穷项相加以后就不可导了呢?

http://baike.baidu.com/link?url= ... 6An_Sd-YppxVtyuUFTI

感觉不是太理解,
我总感觉每一项都可导,然后相加也可导,
可是这个函数每一项都可导,但是相加后就不可导了

kastin

答案在你的签名里。