1. The problem statement, all variables and given/known data Is the set of invertible 3x3 matrices a subspace of 3x3 matrices? 2. Relevant equations 3. The attempt at a solution I think no - the 'neutral 0 element' is not in the subset since the 3x3 0 matrix is not in the subset. Am I right? The book says it's not a subspace because it's not closed under addition, but I'm not sure if my reason is also correct.