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# C4 vectors help! watch

1. I am doing this vectors question an der I am really stuck on 1c)! Please help
http://www.southwolds.co.uk/user/59/49197.pdf
The answer to 1a) is R = (3,4,6). 1c): q= 2 or -4
Many thanks ☺
2. (Original post by PuffyPenguin)
http://www.southwolds.co.uk/user/59/49197.pdf
The answer to 1a) is R = (3,4,6). 1c): q= 2 or -4
Many thanks ☺
You know P, you know R, and you can express Q as

The triangle's area is given by (since it's right-angled). Evaluate it in terms of , set it equal to and solve the quadratic for the two values of
3. (Original post by RDKGames)
You know P, you know R, and you can express Q as

The triangle's area is given by (since it's right-angled). Evaluate it in terms of , set it equal to and solve the quadratic for the two values of
I've done that but I keep getting an answer of 3?!
I got the length of PR to be 6 so the length of RQ should be 3root5.
The length/ modulus of the direction vector is root5, suggesting q is 3. I think I need to use (1,5,6) in some way but I'm not sure how.
4. (Original post by PuffyPenguin)
I've done that but I keep getting an answer of 3?!
I got the length of PR to be 6 so the length of RQ should be 3root5.
The length/ modulus of the direction vector is root5, suggesting q is 3. I think I need to use (1,5,6) in some way but I'm not sure how.
- correct.

- not sure where you are pulling this from.

As I said, we know R and we can express Q in terms of . Hence which has magnitude....?
5. (Original post by RDKGames)
- correct.

- not sure where you are pulling this from.

As I said, we know R and we can express Q in terms of . Hence which has magnitude....?
1/2 x 6 x mod RQ = 9 root 5
If you divide by 3 you get 3 root 5 for mod RQ.
I've got that the magnitude of RQ = root(5q^2 + 10q + 5) so =q+1? But this doesn't give you the value of q
6. I tried to post a picture of my working but it wouldn't upload, sorry
7. (Original post by PuffyPenguin)
1/2 x 6 x mod RQ = 9 root 5
If you divide by 3 you get 3 root 5 for mod RQ.
I've got that the magnitude of RQ = root(5q^2 + 10q + 5) so =q+1? But this doesn't give you the value of q
so

Hence

Solve for the two values of q.
8. (Original post by RDKGames)
so

Hence

Solve for the two values of q.
Aah thank you, that makes sense. I don't think I was using the mod correctly at the end
Thank you!!

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