c = |AB| = |[6, 3, 6]| = 9
b = |AC| = |[4, 5, -2]| = 3·√5
a = |BC| = |[-2, 2, -8]| = 6·√2
Hier die drei gängigsten Verfahren:
Mit Winkel
COS(φ) = [6, 3, 6]·[4, 5, -2]/(ABS([6, 3, 6])·ABS([4, 5, -2])) --> φ = 63.43°
A = 1/2·9·3·√5·SIN(63.43°) = 27.00
Satz von Heron
A = √(1/2·(6·√2 + 3·√5 + 9)·(1/2·(6·√2 + 3·√5 + 9) - 6·√2)·(1/2·(6·√2 + 3·√5 + 9) - 3·√5)·(1/2·(6·√2 + 3·√5 + 9) - 9)) = 27
Kreuzprodukt
A = 1/2·ABS([6, 3, 6] ⨯ [4, 5, -2]) = 27