摘要: Suppose$ f$ has a second derivative everywhere,and that $ f^{''}+f=0$.$ f(0)=0$,$ f^{'}(0)=0$.Then $ f=0$.Proof:Let me first prove that $ \forall x\in... 阅读全文
posted @ 2012-09-28 15:14 叶卢庆 阅读(306) 评论(0) 推荐(0)
摘要: Suppose$ f$ has a second derivative everywhere,and that $ f^{''}+f=0$.$ f(0)=0$,$ f^{'}(0)=0$.Then $ f=0$.Proof:Let me first prove that $ \forall x\in... 阅读全文
posted @ 2012-09-28 15:14 叶卢庆 阅读(162) 评论(0) 推荐(0)
摘要: 设$f:X\to Y$是可逆函数,反函数为$f^{-1}:Y\to X$.设$x_0\in X,y_0\inY$,且$y_0=f(x_0)$(它蕴含$x_0=f^{-1}(y_0)$).如果$f$在$x_0$处可微,且$f^{-1}$在$y_0$处可微,则 \begin{equation} ... 阅读全文
posted @ 2012-09-28 13:53 叶卢庆 阅读(586) 评论(0) 推荐(0)
摘要: 设$f:X\to Y$是可逆函数,反函数为$f^{-1}:Y\to X$.设$x_0\in X,y_0\inY$,且$y_0=f(x_0)$(它蕴含$x_0=f^{-1}(y_0)$).如果$f$在$x_0$处可微,且$f^{-1}$在$y_0$处可微,则 \begin{equation} ... 阅读全文
posted @ 2012-09-28 13:53 叶卢庆 阅读(587) 评论(0) 推荐(0)