My other thread might be useful: http://www.mathhelpforum.com/math-he...subspaces.htmlLet . Suppose further that is a subsapce of spanned by vectors and , and is a subspace of spanned by .

Determine and .

Sifting and gives those two vectors. Hence .

Similarly .

Since we know that is a subspace of .

Therefore and .

Is this it? This question was worth 10 marks but my answer is remarkably small!