1 2 O 1 Let A = 2 3 1 ,b = 0 ,where a is some real number. 0 1 1 a (a) (6 points) Determine the value of a such that the equation AX = b is consistent. Justify your answer and show all your work. (You cannot only write down the answer.) (b) (3 points) Using the choice of a in part (a), let S be the solution set of the equation AX = b, that is, S = {u e R3 : Au = b}. Is S a subspace of R3? Briey explain your answer. (You cannot only write down the answer.)