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Title
Let $A\subseteq\mathbb{R}^n$, $\vec{a}\in \text{int}(A)$, $f:A\to\mathbb{R}$, and $B_{\delta}(\vec{a})\in A$ for some $\delta >0$. Suppose that for some $i, j\in\{1,2, \dots, n\}$, the partial derivatives $\frac{\partial f}{\partial x_i}$, $\frac{\delta f}{\delta x_j}$, $\frac{\delta^2 f}{\delta x_j \delta x_i}$, $\frac{\partial^2 f}{\partial x_i \partial x_j}$ exists on some $B_{\delta}(\vec{a})$. If $\frac{\partial ^2 f}{\partial x_j \partial x_i}$ and $\frac{\partial ^2 f}{\partial x_i \partial x_j}$ are both continuous at $\vec{a}$, then $$\begin{align*} \frac{\partial ^2 f}{\partial x_j\partial x_i}(\vec{a})=\frac{\partial^2 f}{\partial x_i\partial x_j}(\vec{a}) \end{align*}$$Concepts
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Coming soonTitle
Let $A\subseteq\mathbb{R}^n$, $\vec{a}\in \text{int}(A)$, $f:A\to\mathbb{R}$, and $B_{\delta}(\vec{a})\in A$ for some $\delta >0$. Suppose that for some $i, j\in\{1,2, \dots, n\}$, the partial derivatives $\frac{\partial f}{\partial x_i}$, $\frac{\delta f}{\delta x_j}$, $\frac{\delta^2 f}{\delta x_j \delta x_i}$, $\frac{\partial^2 f}{\partial x_i \partial x_j}$ exists on some $B_{\delta}(\vec{a})$. If $\frac{\partial ^2 f}{\partial x_j \partial x_i}$ and $\frac{\partial ^2 f}{\partial x_i \partial x_j}$ are both continuous at $\vec{a}$, then $$\begin{align*} \frac{\partial ^2 f}{\partial x_j\partial x_i}(\vec{a})=\frac{\partial^2 f}{\partial x_i\partial x_j}(\vec{a}) \end{align*}$$Concepts
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Coming soon
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