Question Number 109787 by Rdk96 last updated on 25/Aug/20
$${How}\:{to}\:{prove}\:{that}\:\bigtriangledown×\left(\bigtriangledown×{E}\right)=\:\bigtriangledown\bigtriangledown.{E}−\bigtriangledown^{\mathrm{2}} {E},\:{where}\:{E}\:{is}\:{the}\:{eletric}\:{field}? \\ $$