通过将问题化为非线性算子方程，推导出算子的形式导数，给出了线性化问题解的等价表达。
By reducing the MREIT problem to a nonlinear operator equation, the formal derivative of the operator and the formula of solution for linearization problem are given.
首先，简要介绍了三种主要的求和方法。然后，根据高阶等差数列通项的特性，利用新定义的形式导数列对其进行了有效的探讨。
We first introduce three methods of finding the sum of the first n terms for an arithmetic sequence of higher order, and then display another method by some formal derivatives of which are defined.
针对对称导数、对称偏导数，给出了一些新形式的微分中值定理。
In this paper, symmetric derivative and symmetric partial derivative are researched and some new differential mean value theorems are defined.
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