C4 Vectors help

Hey guys, I just needed some help on question 8 b) ii) in the C4 Jan 2011 paper. I've got as far as finding the values for p, but I don't understand why they choose p=5/7 instead of p=1. Thanks

EDIT :
Sorry I was in a bit of a rush when i posted this. Its for the AQA exam board.
http://filestore.aqa.org.uk/subjects/AQA-MPC4-W-QP-JAN11.PDF

Thanks again.

(edited 9 years ago)

Reply 1

BabyMaths

Original post by zeb786

Hey guys, I just needed some help on question 8 b) ii) in the C4 Jan 2011 paper. I've got as far as finding the values for p, but I don't understand why they choose p=5/7 instead of p=1. Thanks

A link to the paper would help us to help you. :smile:

Reply 2

krisshP

Original post by zeb786

Hey guys, I just needed some help on question 8 b) ii) in the C4 Jan 2011 paper. I've got as far as finding the values for p, but I don't understand why they choose p=5/7 instead of p=1. Thanks

Original post by BabyMaths

A link to the paper would help us to help you. :smile:

http://examsolutions.net/a-level-maths-papers/Edexcel/Core-Maths/Core-Maths-C4/2011-January/paper.php

There's no q8 even on the paper.

Reply 3

BabyMaths

Original post by krisshP

There's no q8 even on the paper.

So it's from another paper which I probably have but I'm not going to check them all.. :tongue:

Reply 4

krisshP

Original post by BabyMaths

So it's from another paper which I probably have but I'm not going to check them all.. :tongue:

I just checked a bunch of C4 papers using the Examsolutions C4 papers page, but I can't find q8bii in any of them. The closest to getting there is q8b but not q8bii found.

Reply 5

maggiehodgson

Original post by zeb786

Hey guys, I just needed some help on question 8 b) ii) in the C4 Jan 2011 paper. I've got as far as finding the values for p, but I don't understand why they choose p=5/7 instead of p=1. Thanks

I don't have the question you're asking about but sometimes, if you use one of the versions of p then it would lead to a point that has already been used in the question so your only option is for the other value of p.

Try that but otherwise you'll have to find the exact question.

Reply 6

zeb786

Original post by BabyMaths

A link to the paper would help us to help you. :smile:

http://filestore.aqa.org.uk/subjects/AQA-MPC4-W-QP-JAN11.PDF

Heres the link. :smile:

Thank you

Reply 7

zeb786

Original post by maggiehodgson

http://filestore.aqa.org.uk/subjects/AQA-MPC4-W-QP-JAN11.PDF

Heres the Link.

Thank you :smile:

Reply 8

BabyMaths

Original post by zeb786

http://filestore.aqa.org.uk/subjects/AQA-MPC4-W-QP-JAN11.PDF

Heres the Link.

Thank you :smile:

In my attached diagram you can see the two points on L2 where C would be the correct distance from B but the point where my pink lines intersect is too far from D.

AQA C4 8bii Jan 2011.png

With p=1 you would have |DC| = |AB| resulting in a parallelogram. For the trapezium we need |DC|<|AB| and so p<1.

Reply 9

zeb786

Original post by BabyMaths

In my attached diagram you can see the two points on L2 where C would be the correct distance from B but the point where my pink lines intersect is too far from D.

AQA C4 8bii Jan 2011.png

With p=1 you would have |DC| = |AB| resulting in a parallelogram. For the trapezium we need |DC|<|AB| and so p<1.

I understand it a bit better now thank you. But how would i know that p=1 will give the point where the pink lines intersect. Should i sub in the values for both p values in the l2 vector equation and choose the one that gives me a closer distance? And can there ever be a point where C can be two different co-ordinates , like for example in another shape?