a)
A = [1, 6, 4]
B = [-1, 4, -2]
C = [4, -2, 2]
AB = B - A = [-1, 4, -2] - [1, 6, 4] = [-2, -2, -6]
BC = [5, -6, 4]
CA = [-3, 8, 2]
AB + BC + CA = [-2, -2, -6] + [5, -6, 4] + [-3, 8, 2] = [0, 0, 0] = O
Damit ist
A + (AB + BC + CA) = A
b)
U = |AB| + |BC| + |CA| = √(22 + 22 + 62) + √(52 + 62 + 42) + √(32 + 82 + 22) = √44 + √77 + √77 ≈ 24.18 LE