For a,b∈R3\mathbf{a}, \mathbf{b} \in \mathbb{R}^3a,b∈R3, which of the following is a valid formula for ∥a×b∥\|\mathbf{a} \times \mathbf{b}\|∥a×b∥?
∥a∥∥b∥cosθ\|\mathbf{a}\|\|\mathbf{b}\|\cos\theta∥a∥∥b∥cosθ
∥a∥∥b∥sinθ\|\mathbf{a}\|\|\mathbf{b}\|\sin\theta∥a∥∥b∥sinθ
∥a∥2+∥b∥2\|\mathbf{a}\|^2 + \|\mathbf{b}\|^2∥a∥2+∥b∥2
∥a∥⋅∥b∥⋅tanθ\|\mathbf{a}\| \cdot \|\mathbf{b}\| \cdot \tan\theta∥a∥⋅∥b∥⋅tanθ