1. The problem statement, all variables and given/known data Show that u, v, w lie in the same plane in R3 if and only if u · (v × w) = 0. 2. Relevant equations 3. The attempt at a solution if u · (v × w) = 0, then u is orthogonal to vxw, and vxw is orthogonal to v and w. therefore, u must lie in the same plane determined by v and w (i.e. they are coplanar) Is this correct? Also, how would i describe this proof mathematically? Thanks!