jika vektor r=5i + 2j -2k dan s = 2i - cj +k saling tegak lurus, maka nilai c adalah :

r dan s saling tegak lurus, maka
r . s = 0
(5,2,-2) . (2,-c,1) = 0
10 - 2c - 2 = 0
2c = 8
c = 4

r = 5i + 2j - 2k = (5, 2, -2)
s = 2i - cj + k = (2, -c, 1)

r tegak lurus s maka
r . s = 0
5(2) + 2(-c) + (-2)(1) = 0
10 - 2c - 2 = 0
8 - 2c = 0
-2c = -8
c = -8/-2 = 4