tentukan kosinus sudut antara vektor a=3i+7j+2k

Cos α = a. b / |a| |b|

a = 3i + 7j + 2k = (3, 7, 2)
b = i + j - 6k = (1, 1, -6)

a. b = (3, 7, 2) (1, 1, -6) = (3 + 7 - 12) = -2
|a|= √(3)² + (7)² + (2)² = √9 + 49 + 4 = √62
|b| = √1² + 1² + -6² = 1 + 1 + 36 = √38

cos α = -2/√38 √62
cos α = -1 / 589 √589