I need the step

9. Determine if the vectors a = [5,1,-2]. b =[-2,3,1] and c = [11,9,-4] are coplanar. [6] 10. Given a = [3,4,3] and b = [1,-2,5] a. Calculate the angle between a and b. [3] b. If c =[1,-3,/], find / so that a and c are perpendicular. [3] 10