3. Let X be N3 (u, E) with 2 2 O CO N E = 2 3 1 (a) Is X1 and X3 independent? Explain. (b) Is (X1, X3) and X2 independent? Explain. (c) Find a 2 x 1 vector a = a1 such that X2 and X2-aT X 1 are indepen a2 X 3 dent by listing the equations that a needs to fullfill. Is a unique? If a is unique, write down the value of a. If a is not unique, write down the form of a which will meet the requirements