Besar sudut antara vektor a = 2i – j + 3k dan b = i + 3j – 2k adalah ….

Vektor
A =(2, -1, 3)
B = (1, 3 ,-2)

|a|= √(2²+(-1)²+(3)² = √14
|b| = √(1²+3²+(-2)²) = √14

a.b = 2(1) -1(3) +3(-2)  = -7

cos(a,b) = a.b /|a||b| = -7/(√14)(√14) = -7/14 = -1/2
cos(a,b) = - cos 60 = cos (180-60) = cos 120
<(a,b) = 120°