Hi,

It does not make sense : is at the same time the subspace spanned by and and the subspace spanned by and ... but these subspaces may be different !

Here is what I think they meant :

problem:Suppose that and are vectors and is a subspace in a vector space ;

let be the subspace spanned by and , and let be the subspace spanned by and .

Prove that if is in but not in , then is in .