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# Vector Question- Alevel watch

1. A,B and C have position vectors (9i-2j+k),(6i+2j+6k) and (3i+pj+qk) respectively, were p and q are constants.

find in vector form the equation of the line which passes through A and B. Given that C lies on l.

What I did was (b-a) to get (-3i+4j+5k) as the direction vector But the answer had (3i-4j-5k)...why? I am assuming it is something to do with C but I dont know
2. (Original post by joyoustele)
A,B and C have position vectors (9i-2j+k),(6i+2j+6k) and (3i+pj+qk) respectively, were p and q are constants.

find in vector form the equation of the line which passes through A and B. Given that C lies on l.

What I did was (b-a) to get (-3i+4j+5k) as the direction vector But the answer had (3i-4j-5k)...why? I am assuming it is something to do with C but I dont know
You can use any direction vector parallel to -3,4,5 so both answers are fine. Textbooks will only give one answer but there are infinitely many ways you can write the vector equation of a line.

Are you sure the “Given that C lies on l” was part of the same question? It seems irrelevant.
3. (Original post by Notnek)
You can use any direction vector parallel to -3,4,5 so both answers are fine. Textbooks will only give one answer but there are infinitely many ways you can write the vector equation of a line.

Are you sure the “Given that C lies on l” was part of the same question? It seems irrelevant.
Oh, you're right, C is part of the next question.

Thanks

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