Find out whether each of the following subsets is a subspace of the vector space indicated
a) The set of all matrices in the vector space M22 whose determinant equals 0 where M22 is the set of all 2X2 matrices
b) The set of all vectors in teh vector space R4 for which x1=x4
c) The set of all functions of the form f(0)=0 in the vector space consisting of all real-valued functions which are defined on the entire real number line