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6. (5+5+5+5) (a) Find the direction cosines of the vector v = i t j + k. (b) Show that the vectors v1 = (1, 0, 1) and v2 = (-1, 1, 1) are orthogona to each other. (c) Find a vector that has the same direction as the vector (5, 2, -3) an has length 11. (d) Let a and b be two vectors such that the scalar projection of b on a i equal to b (modulus of b). Find the angle between a and b