a)
[20, 40, 2] + r·[a - 12, - 2·a - 20, 4·a - 2] = [11, 14, 12] --> a = 3 ∧ r = 1
b)
[20, 40, 2] + r·[a - 12, - 2·a - 20, 4·a - 2] = [13, 20, 0] + s·([7, 17, 6] - [13, 20, 0]) --> a = 1 ∧ r = 1 ∧ s = 2/3
c)
r·[a - 12, - 2·a - 20, 4·a - 2] = [12, 12, 16] - [20, 20, 0] → Keine Lösung
Keiner der Strahlen ist parallel zur Seitenkante BS.