9. Determine if the vectors a = [-1, 2, 1], b = [-2, 4, 2], and & = [12, 8, 1] are coplanar. [6] 10. Given a = [5, 6, 4] and b = [-1,2, 7]: a) Calculate the angle between a and b. [3] b) If c = [2, -5, t], find t so that a and c are perpendicular. [3] Page 11 of 13