You are Here: Home

# P3 vectors.. eeeeeassy question!! watch

1. I must be doing something really stupid, but for some reason it's not working.

P3 heinemann book page 192, question 53 part a)

With respect to an origin, O, the position vectors of the points L and M are 2i - 3j + 3k and 5i + j + ck where c is a constant
The point N is such that OLMN is a rectangle.

find the value of c.

Now surely with it being a rectangle, OL and OM must be perpendicular.
therefore the dot product of these vectors must be 0.

so 2i - 3j + 3k . 5i + j + ck
10 - 3 + 3c = 0
c = -7/3

but the answer is 5! what the hell?
It must be obvious, but I reckon I've lost it doing too much revision.. argh! help me out someone!
2. i've got the same as u.........maybe misprint in the book? as they always get answers wrong.....
3. (Original post by wonkey)
i've got the same as u.........maybe misprint in the book? as they always get answers wrong.....

but actually.......u never get fractions as an answer tho, the co-efficient is always an integer...hmmmm
4. Draw a diagram, OL and OM will not be perpendicular. OL and ON will.
5. The book is correct btw.
6. (Original post by JamesF)
Draw a diagram, OL and OM will not be perpendicular. OL and ON will.
but it's a rectangle? surely all the edges are at rightangles?
can you please explain in more detail?
7. someone just explained this problem in another thread..look further down the page

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 7, 2004
Today on TSR

### Uni league tables

Do they actually matter?

### University open days

• University of Exeter
Wed, 24 Oct '18
Wed, 24 Oct '18
• Northumbria University
Wed, 24 Oct '18
Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE