一级标题 一级标题 一级标题 一级标题 一级标题 一级标题 ∂nf(x1,x2,…,xm)∂x1∂x2…∂xn=∑i1=1m∑i2=1m…∑in=1m∂nf∂xi1∂xi2…∂xin⋅∂xi1∂x1⋅∂xi2∂x2…∂xin∂xn\frac{\partial^{n} f(x_1, x_2, \ldots, x_m)}{\partial x_1 \partial x_2 \ldots \partial x_n} = \sum_{i_1=1}^{m} \sum_{i_2=1}^{m} \ldots \sum_{i_n=1}^{m} \frac{\partial^n f}{\partial x_{i_1} \partial x_{i_2} \ldots \partial x_{i_n}} \cdot \frac{\partial x_{i_1}}{\partial x_1} \cdot \frac{\partial x_{i_2}}{\partial x_2} \ldots \frac{\partial x_{i_n}}{\partial x_n}∂x1∂x2…∂xn∂nf(x1,x2,…,xm)=i1=1∑mi2=1∑m…in=1∑m∂xi1∂xi2…∂xin∂nf⋅∂x1∂xi1⋅∂x2∂xi2…∂xn∂xin