一道高数题，此函数于x=0点处有定义。
\u9ad8\u6570\u8ba8\u8bba\u51fd\u6570\u96f6\u70b9\u95ee\u9898\u7b2c\u4e00\u4e2a\u9634\u5f71\u662f\u6839\u636e\u51fd\u6570\u6781\u9650\u5c40\u90e8\u4fdd\u53f7\u6027\u5f97\u5230\u7684\uff0c\u5177\u4f53\u7684\u5b9a\u4e49\u770b\u524d\u9762\u3002
\u7b2c\u4e00\u4e2a\u9634\u5f71\u5229\u7528\u62c9\u683c\u6717\u65e5\u5b9a\u7406
f(x)=f(x0)+f'(\u03be)(x-x0)
\u2265f(x0)+\u03b2(x-x0)/2 (f'(\u03be)\u2264\u03b2/2<0\uff0c\u800cx\u2264x0\uff0c\u4ece\u800c\u6709x-x0\u22640)
\u5bf9\u4e0a\u4e0d\u7b49\u5f0f\u6c42\u6781\u9650\uff0c\u663e\u7136\u6709x\u8d8b\u4e8e\u8d1f\u65e0\u7a77\u65f6\uff0c limf(x)\u8d8b\u4e8e\u6b63\u65e0\u7a77\u3002
epsilon\u5c31\u597d\u6bd4\u4e00\u4e2a\u6807\u51c6\uff0c\u8fd9\u4e2a\u6807\u51c6\u53ef\u4ee5\u4efb\u610f\u7ed9\u51fa\uff0c\u4f46\u7ed9\u51fa\u540e\u5c31\u5fc5\u987b\u786e\u5b9a\u3002\u8bc1\u660e\u6781\u9650\u7684\u672c\u8d28\u5c31\u662f\u6839\u636e\u90a3\u4e2a\u7ed9\u5b9a\u7684epsilon\u627e\u51fadelta\uff0c\u6240\u4ee5delta\u5f80\u5f80\u548cepsilon\u6709\u5173\u3002\u627e\u5230\u5c31\u5f97\u8bc1\u3002
\u7406\u89e3\u7684\u5173\u952e\u662f\u201c\u4efb\u610f\u201d\u548c\u201c\u7ed9\u5b9a\u201d\u7684\u5173\u7cfb\uff0cepsilon\u65e2\u662f\u4efb\u610f\u7684\uff0c\u53c8\u662f\u7ed9\u5b9a\u7684\u3002
极限不存在。因为f(x)在x趋于0时左右极限不相等。存在f(x)在某点不连续，但f(x)在该点极限存在的函数。
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