Tolong di jawab soal vektor. Lupa soal beginian : plissss

Materi: Vektor

AB = p = B - A = (4, 1, -1) - (2, 4, -2) = (2, -3, 1)
CD = q = D - C = (8, 2, -1) - (7, 0, 2) = (1, 2, -3)
p.q = (2, -3, 1).(1, 2, -3) = (2×1)+(-3×2)+(1×-3)=-7
|p| = akar (2^2+(-3)^2+1^2) = akar 14
|q| = akar 14
sehingga
cos (alfa) = p.q/|p|.|q| = -7/14 = -1/2
alfa = arc cos -1/2 = 120 derajat (Jawaban A)

Matematika X SMA
→→ Vektor ←←

Pembahasan :
P = AB = b - a
P = [4 1 -1] - [2 4 -2]
P = [2 -3 1]

Q = CD = d - c
Q = [8 2 -1] - [7 0 2]
Q = [1 2 -3]

Sudutnya misalkan β, maka...
Cos β = (p . q)/(|p| |q|)
Cos β = [2.1 + (-3).2 + 1(-3)]/[√14 √14]
Cos β = (2 - 6 - 3)/14
Cos β = -7/14
Cos β = -1/2
Cos β = Cos 120°
β = 120°