x Turn on thread page Beta
 You are Here: Home >< Maths

# edexcel FP3 vectors question. watch

1. Hi,

fairly easy vectors question, im looking for a nice, neat way to answer it. if anyone could help, that would be awesome.

the plane P has equation r.(i + j - k) = 4
the line l1, with equation r = 2i + 3j + k + t(-i + 2j + k) lies in the plane P.
show that the line l2, with equation r = -i + 2j + 4k + s(-i + 2j + k) is parallel to the plane P.

to me it seems fairly obvious that because l1 is parallel to l2, l2 must be parallel to P, but i wanted to say something less lame than that. i was thinking is there some way to use the scalar product to make it obvious?? help much appreciated - rep up for grabs, if you are in to that kind of thing...
2. you can just say because the l1 and l2 have have the same direction vector they must be parallel, and since l1 lies in the plane they are are also parallel, i dont see the problem in this
3. If you were being strict about it you would do the cross product of the two direction vectors of the lines and show that that does indeed come to zero.
4. i did it like that in the end, thanks.

I just thought maybe there was a way of using the equation of the plane, but maybe not.

Thank you!!! xx
5. Just a thought: Do you need to show that l2 is not in the plane, or are you allowed to include that as a possibility within "parallel to".

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: February 9, 2010
Today on TSR

### Any tips for freshers...

who are introverts?

### More snow?!

Discussions on TSR

• Latest
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest

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