4. Vector u is a unit vector orthogonal to vectors a and b , where a : i+ j k, b : 21' j. Then the coordinates of vector u in the basis {1', j, k} are (a) [n _i _i] J3\" JE ' 45 (b) (1, 2,3) (c) None of the above is true 5. Expression -(bxa) is {a} is meaningless (b) designates a vector {c} is equal to {J 6. If a and b are unit vectors, then vector v = a b (a) is a zero-vector (b) is such a vector that \"v\" 1: 1 (c) is orthogonal to the vector .1: + b