title: How do I retrieve the angle between two vectors 3D?
body: <p>I am new in python.
  I have two vectors in 3d space, and I want to know the angle between two</p>
  
  <p>I tried:</p>
  
  <pre><code>vec1=[x1,y1,z1]
  
  vec2=[x2,y2,z2]
  
  angle=np.arccos(np.dot(vec1,vec2)/(np.linalg.norm(vec1)*np.linalg.norm(vec2)))
  </code></pre>
  
  <p>but when change the order, vec2,vec1 obtain the same angle and no higher.
  I want to give me a greater angle when the order of the vectors changes.</p>