📝 题目
6.6.4 证明: (1) $\operatorname{rot}\left( {\operatorname{grad}u}\right) = 0$ ; (2) $\operatorname{div}\left( {\operatorname{rot}\mathbf{F}}\right) = 0$ .
6.6.4 证明: (1) $\operatorname{rot}\left( {\operatorname{grad}u}\right) = 0$ ; (2) $\operatorname{div}\left( {\operatorname{rot}\mathbf{F}}\right) = 0$ .