Find if the following are vector spaces over R(all real #). If the set isn't a vector space over R then state why it is not.
a.) The set of non-singular 2x2 matrices with real entries and the standard operations.
b.) The set of all convergent infinit series with the standard operations
c.) The set of all 2x2 matrices with real entries of the form [ a 2 ; b c] with standard operations
d.) The null space of a real nxn matrix A with the standard operations.