一、题目
已知,有 $u(x, y)$ $=$ $u(\sqrt{x^{2} + y^{2}})$, $r$ $=$ $\sqrt{x^{2} + y^{2}}$ $>$ $0$.
并且已知函数 $u(x, y)$ 有二阶连续的偏导数,要求计算:
$\frac{\partial u}{\partial x}$、$\frac{\partial ^{2} u}{\partial x^{2}}$、$\frac{\partial u}{\partial y}$、$\frac{\partial ^{2} u}{\partial y^{2}}$.
继续阅读“一个复合函数求二阶偏导的例题:$u(x, y)$ $=$ $u(\sqrt{x^{2} + y^{2}})$”