Diketahui vektor a = 5 i + m j + 3k,b = n i + 7 j + 2k,dan c = 3 i + m j - k. Jika vektor a tegak lurus b dan vektor b tegak lurus c maka a+2b-c adalah ?

a = <5,m,3>
b = <n,7,2>
c = <3,m,-1>

a.b  = 0
5n + 7m + 6 = 0
 b.c = 0
3n + 7m  -2 = 0

5n + 7m + 6 = 0
3n + 7m  -2 = 0
________________ -
2n + 8 = 0
n = -4

-20 + 7m + 6 = 0
7m = 14
m = 2
 
a + 2b - c = <5,2,3> + <-8,14,4> - <3,2,-1>
= < -6, 14, 8>

-6i + 14j + 8k (C)