1. The problem statement, all variables and given/known data For a fluid flow of velocity u and vorticity w=∆ x u, show that: (u. ∆ )u=-u x w + ∆(1/2|u|²) Sorry the triangles should be the other way up! 2. Relevant equations ∆(u.v)=(u.∆)v + (v.∆)u +u x (∆ x v) + v x (∆ x u ) 3. The attempt at a solution I need to show this using subscipt notation, but am really stuck, any help?