You are Here: Home >< Maths

# C4 vectors watch

1. will post in a min

2. so basically I need help in C and D

for C
they told the line 2 is parallel to L1 so direction will be same but what will be the points
r=(?)+u(direction)

for D
I have to use modulus but how to find B coordinates ?It is one mark but still I got stuck
3. (Original post by Qer)

so basically I need help in C and D

for C
they told the line 2 is parallel to L1 so direction will be same but what will be the points
r=(?)+u(direction)

for D
I have to use modulus but how to find B coordinates ?It is one mark but still I got stuck
Yes the direction is the same. You only need one point to define the line since you know the direction. You know it passes through B, so find its coordinates since you know its related to the point A, namely
4. (Original post by RDKGames)
Yes the direction is the same. You only need one point to define the line since you know the direction. You know it passes through B, so find its coordinates since you know its related to the point A, namely
thanks
5. so if A was for instance ( 2, -3, 8 ) then B would be ( 6, -9, 24 )
6. can you guys also help me in part e

I draw a diagram something like that
7. (Original post by Qer)
can you guys also help me in part e

I draw a diagram something like that
It says that and are perpendicular. This means that the angle between the vector and the direction vector of is 90, which hence implies that the dot product between the two is 0.

You know the dir. vector already.
To get the vector , just begin by saying that X has general coordinates for some since it lies on .
So, just use the dot product condition mentioned earlier to get the value of that defines X, then just find the length of that vector.

A DIFFERENT APPROACH would be to find cosine of the acute angle between the line and vector . Then use the fact that (seen clearly from your diagram, in the right-angled triangle OXB)
8. (Original post by RDKGames)
It says that and are perpendicular. This means that the angle between the vector and the direction vector of is 90, which hence implies that the dot product between the two is 0.

You know the dir. vector already.
To get the vector , just begin by saying that X has general coordinates for some since it lies on .
So, just use the dot product condition mentioned earlier to get the value of that defines X, then just find the length of that vector.

A DIFFERENT APPROACH would be to find cosine of the acute angle between the line and vector . Then use the fact that (seen clearly from your diagram, in the right-angled triangle OXB)

thank you

### Related university courses

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 18, 2018
Today on TSR

### Top unis in Clearing

Tons of places at all these high-ranking unis

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