Hi all, I was going through the derivation for the electromagnetic field of point charges by Griffith(Introduction to electrodynamics page 437). I'm missing minus sign somewhere: The book says that:[itex]\nabla(\vec{n}\cdot\vec{v})=\vec{a}(\vec{n}\cdot \nabla tr)+\vec{v}-\vec{v}(\vec{v}\cdot\nabla tr)-\vec{n}\times(\vec{a}\times \nabla tr)+\vec{v}\times (\vec{v}\times \nabla tr)[/itex] Using the rule for triple cross products gives: [itex]\vec{v}+(v^{2}-\vec{n}\cdot\vec{a})\nabla tr[/itex] However is should be: [itex]\vec{v}+(-v^{2}+\vec{n}\cdot\vec{a})\nabla tr[/itex] I'm sure Im missing something. Thanks