1. The problem statement, all variables and given/known data Let V be the spcae of all 3x3 matrices with real entries. Is W, the set of all 3x3 lower triangular matrices, a subspace of V? Why or why not? 2. Relevant equations 3. The attempt at a solution I just think that all 3x3 lower triangular matrices are included in all 3x3 matrices with real entires. So my answer is that W is a subspace of V. but I don't know correct answer. and I don't know how to explain why I think W is a subspace of V... I think I'm missing an important definition or theorem...?