Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
 You are Here: Home >< Maths

# Vector Line watch

1. Hello,

I'm having trouble answering this question.

Q: Relative to the origin O, the point A has position vector given by OA = i + 2j + 4k. The line l has
equation r = 9i − j + 8k + 3i − j + 2k . Find the position vector of the foot of the perpendicular from A to l. Hence find the position
vector of the reflection of A in l.

I found the position vector of the foot of the perpendicular as 3/2i + 3/2j + 3k.
But I don't understand how to answer the second part.

I appreciate your help.
2. (Original post by Yoshimineb)
Hello,

I'm having trouble answering this question.

Q: Relative to the origin O, the point A has position vector given by OA = i + 2j + 4k. The line l has
equation r = 9i − j + 8k + 3i − j + 2k . Find the position vector of the foot of the perpendicular from A to l. Hence find the position
vector of the reflection of A in l.

I found the position vector of the foot of the perpendicular as 3/2i + 3/2j + 3k.
But I don't understand how to answer the second part.

I appreciate your help.
Your equation for the line has significant typos, to the extent I can't decipher it.

However, for the second part. Draw a diagram. If F is the foot of the perpendicular, then the reflection of A in l, is reached by extending AF by the same length again. I.e. OA + 2AF
3. (Original post by ghostwalker)
Your equation for the line has significant typos, to the extent I can't decipher it.

However, for the second part. Draw a diagram. If F is the foot of the perpendicular, then the reflection of A in l, is reached by extending AF by the same length again. I.e. OA + 2AF

Thank you for your reply,ghostwalker.

I'm sorry for all the typos and my carelessness.As this is my first post, I just copied from a past year paper so I didn't pay much attention to the equations.

Using the equation OA + 2AF, I got the correct answer.However, I do not understand why it's the answer.

Could you Explain how you came up with the equation?
4. (Original post by Yoshimineb)
Thank you for your reply,ghostwalker.

I'm sorry for all the typos and my carelessness.As this is my first post, I just copied from a past year paper so I didn't pay much attention to the equations.

Using the equation OA + 2AF, I got the correct answer.However, I do not understand why it's the answer.

Could you Explain how you came up with the equation?
Wow! now I understand what the question is asking.Thank you for your help.

Reply
Submit reply
Turn on thread page Beta
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 8, 2018
Today on TSR

### Four things top students are doing

Over the Easter break

Poll
Useful resources

## Make your revision easier

### 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

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups

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

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.