记向量 p = (p1, p2, p3)a×b = i(a2b3-a3b2) + j(a3b1-a1b3) + k(a1b2-a2b1)(a×b)·c = c1(a2b3-a3b2) + c2(a3b1-a1b3) + c3(a1b2-a2b1) = |a1 a2 a3||b1 b2 b3||c1 c2 c3|
