The vectors vec(u) and vec(v) are given in terms of the basis vectors vec(a) , vec(b) and vec(c) as follows: vec(u) =3 vec(a) +3 vec(b) −vec(c) vec(v) =vec(a) +2 vec(b) +3 vec(c) Prove that vec(u) and vec(v) are orthogonal vectors

Nelson Jennings

Nelson Jennings

Answered question

2022-07-18

Prove that u and v are orthogonal vectors
The vectors u and v are given in terms of the basis vectors a , b and c as follows:
u = 3 a + 3 b c
v = a + 2 b + 3 c
I've tried u . v to see if their dot product equals to 0, but it does not. Am I missing something?
It was given that a , b , and c form a basis in R 3 .
It was also given that:
| a | = 1 , | b | = 2 , | c | = 3

Answer & Explanation

Steppkelk

Steppkelk

Beginner2022-07-19Added 11 answers

With these changes,
u , v = 3 a + 3 b c , a + 2 b + 3 c = ! 3 a , a + 3 b , 2 b + c , 3 c = 3 a , a + 6 b , b 3 c , c = 3 1 2 + 6 2 2 3 3 2 = 0
But you still need that the basis is orthogonal.
makaunawal5

makaunawal5

Beginner2022-07-20Added 5 answers

If you expand u v you find 9 a b + 8 a c + 7 b c
There is no reason for this to be zero in general, unless we also know that a,b,c are orthogonal. So my guess is that in the instructions for the problem there was the information that a,b,c are orthogonal.

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