a×b=|ijka1a2a3b1b2b3|=(a2⁢b3-a3⁢b2)⁢i+(a3⁢b1-a1⁢b3)⁢j+(a1⁢b2-a2⁢b1)⁢k=∥a∥⁢∥b∥⁢(sin⁡θ)⁢n,