若是 |a| = 1, |b| = 2, 向量 a · b = -√3, a · b = |a| |b| cosθ = 2cosθ = -√3, cosθ = - √3/2则 |a×b| = |a| |b| sinθ = 2 · 1/2 = 1
若是 |a| = 1, |b| = 2, 向量 a · b = -√3,a · b = |a| |b| cosθ = 2cosθ = -√3, cosθ = - √3/2则 |a×b| = |a| |b| sinθ = 2 · 1/2 = 1