a)
|[4,4,3]| = √41
|[0,1,4] - [6,0,5]| = √38
|[4,4,3] + 2[0,1,4]| = √173
|[0,1,4] - 2[4,4,3] + [6,0,5]| = √62
|[4,4,3] + [0,1,4] + [6,0,5]| = √269
|2[4,4,3] - [0,1,4] - 2[6,0,5]| = √129
b)
|([5,10,15] - [2,2,1]) - ([4,6,5] - [3,a,0])| = 11 --> a = -8 ∨ a = 4
