Which statement about dot products in Rn\mathbb{R}^nRn is true?
u⋅u<0\mathbf{u} \cdot \mathbf{u} < 0u⋅u<0 is possible for nonzero u\mathbf{u}u
u⋅u=0\mathbf{u} \cdot \mathbf{u} = 0u⋅u=0 if and only if u=0\mathbf{u} = \mathbf{0}u=0
u⋅u\mathbf{u} \cdot \mathbf{u}u⋅u can be negative
u⋅v\mathbf{u} \cdot \mathbf{v}u⋅v is always non-negative