5. (4 marks) Let F be a C-vector field on R3 and u ERP be a unit vector. Prove that for every (x, y, z) e R3 (V x F(x, y, z)) . u = lim Fids, where C, is the circle of radius r in R3 centered at (x, y, z) lying in the plane perpendicular to u. 5. (4 marks) Let F be a C-vector field on R3 and u ERP be a unit vector. Prove that for every (x, y, z) e R3 (V x F(x, y, z)) . u = lim Fids, where C, is the circle of radius r in R3 centered at (x, y, z) lying in the plane perpendicular to u