$latex \mathbf{Question:} \text{ Let S be the subspace of } M_{n \times n} \text{(the vector space of all real }\\
n \times n \text{ matrices ) generated by all matrices of the form } AB-BA \text{ with A and B in } \\
M_{n \times n} . \text{ Then dim(S)}=—\\\\
1. n^2\\
2. n^2-1\\
3.2n\\
4. \frac{n(n+1)}{2}$