A set of independent vectors of the whole vector space can be generated, which can uniquely represent any element in the vector space, so it is the representative of this vector space. For example, three mutually perpendicular unit vectors in a spatial coordinate system:

i=( 1，0，0)； j=(0， 1，0)； k=(0，0， 1)

If the vector e 1 e2 is not a * * * line, then the necessary and sufficient condition for the vector r and the plane e 1 e2 * * is that r can be expressed linearly by e 1e2, that is, r=xe 1+ye2, then e1e2 is the basis.