Which of the following is true about u×u\mathbf{u} \times \mathbf{u}u×u for any non-zero vector u\mathbf{u}u?
u×u=0\mathbf{u} \times \mathbf{u} = \mathbf{0}u×u=0
u×u=∥u∥2\mathbf{u} \times \mathbf{u} = \|\mathbf{u}\|^2u×u=∥u∥2
u×u=u\mathbf{u} \times \mathbf{u} = \mathbf{u}u×u=u
u×u\mathbf{u} \times \mathbf{u}u×u is undefined