Paper 3, Section I, A

Vector Calculus
Part IA, 2007

By using suffix notation, prove the following identities for the vector fields A\mathbf{A} and B in R3\mathbb{R}^{3} :

(A×B)=B(×A)A(×B)×(A×B)=(B)AB(A)(A)B+A(B)\begin{gathered} \nabla \cdot(\mathbf{A} \times \mathbf{B})=\mathbf{B} \cdot(\nabla \times \mathbf{A})-\mathbf{A} \cdot(\nabla \times \mathbf{B}) \\ \nabla \times(\mathbf{A} \times \mathbf{B})=(\mathbf{B} \cdot \nabla) \mathbf{A}-\mathbf{B}(\nabla \cdot \mathbf{A})-(\mathbf{A} \cdot \nabla) \mathbf{B}+\mathbf{A}(\nabla \cdot \mathbf{B}) \end{gathered}