Is it necessary that two vectors will always be coplanar

3dvectors

Is it necessary that in 3 dimensions, two vectors will always be coplanar ? My teacher told the class that in 3 dimensions two vectors are always coplanar. But what if we consider two non parallel and non intersecting vectors ? like the ones parallel to 2 skew lines how can these be co planar ?

Another example is consider a cube. Now take one vector that is along the face diagonal of the upper face of the cube and another one that is along the face diagonal of the bottom face (the diagonal that is not in the same direction as the other one). These 2 are not coplanar as well.

Best Answer

You're confusing vectors with line segments and linear spaces with affine spaces.

When you take the example of the cube, you describe line segments. Those are indeed not coplanar. But those are also not vectors.

If you want to visualize (not a good mathematical word by the way...) coplanar vectors, you have to position the origin of those vectors at a common point. If the other vertices of those vectors and the common points are coplanar, then you can say that those vectors are coplanar.

When you apply this logic, you'll get the conclusion that any two vectors are always coplanar. Which by the way is not only true in dimension $3$ but for any dimension $n \ge 2$.