You are Here: Home >< Maths

# Edexcel A2 C4 Mathematics June 2015 - Official Thread Watch

1. (Original post by Pineappleface317)
Hey I'm actually OCR but I couldn't find an OCR C4 2015 thread but I'm guessing you guys do vectors??
Could someone help me with this question:

Find a unit vector that is perpendicular to both 4i + 10j - 3k and 5i - 9j + 7k

All I have so far is:
4a + 10b - 3c = 0
and
5a - 9b + 7c = 0

(ai + bj + ck being my unknown unit vector)

Thanks
Hint: it says "unit" vector

Posted from TSR Mobile
2. (Original post by Pineappleface317)
Hey I'm actually OCR but I couldn't find an OCR C4 2015 thread but I'm guessing you guys do vectors??
Could someone help me with this question:

Find a unit vector that is perpendicular to both 4i + 10j - 3k and 5i - 9j + 7k

All I have so far is:
4a + 10b - 3c = 0
and
5a - 9b + 7c = 0

(ai + bj + ck being my unknown unit vector)

Thanks
Maybe use c=1 and solve

Posted from TSR Mobile
3. (Original post by aersh8)
Hint: it says "unit" vector

Posted from TSR Mobile
A very poor hint - if it could be considered a hint at all.
4. (Original post by Medicjug)
Maybe use c=1 and solve

Posted from TSR Mobile
Probably better to use c=0

But c=1 would also give a perpendicular vector - just easier when using c=0
5. (Original post by Medicjug)
Maybe use c=1 and solve

Posted from TSR Mobile
just cross them!!!!!!
6. (Original post by Medicjug)
Maybe use c=1 and solve

Posted from TSR Mobile
So that's just because each component in i k and k is one unit long? So I could make anything one?
Sorry for some reason I can't get my head around vectors ..
7. (Original post by Tow)
Probably better to use c=0

But c=1 would also give a perpendicular vector - just easier when using c=0
How come you can use c=0 ?
8. (Original post by Pineappleface317)
So that's just because each component in i k and k is one unit long? So I could make anything one?
Sorry for some reason I can't get my head around vectors ..
No, think of it this way if som vector is parralel to both it will be a mutiple of some direction vector. We can factor out a multiple such that c=1 leaving a,b not determined as of yet and then adjust the actual vector in the end.

Posted from TSR Mobile
9. (Original post by Tow)
Probably better to use c=0

But c=1 would also give a perpendicular vector - just easier when using c=0
You cant use Z=0 this results in the vector 0,0,0.

Posted from TSR Mobile
10. (Original post by physicsmaths)
You cant use Z=0 this results in the vector 0,0,0.

Posted from TSR Mobile
Oh yeah.

I assumed it would be easier - haven't done this question since we went through the book back in Feb!

But yeah you use c=1 sorry about that xD

It can be anything BUT 0 and obviously 1 would be the easiest choice.
11. (Original post by Tow)
A very poor hint - if it could be considered a hint at all.
To be fair that can be used to form 3 simultaneous equations but that'll just be harder to solve

Posted from TSR Mobile
12. (Original post by Tow)
Oh yeah.

I assumed it would be easier - haven't done this question since we went through the book back in Feb!

But yeah you use c=1 sorry about that xD

It can be anything BUT 0 and obviously 1 would be the easiest choice.
Correct.

Posted from TSR Mobile
13. useful material for the upcoming exams

http://www.thestudentroom.co.uk/show....php?t=3353445

http://www.thestudentroom.co.uk/show....php?t=3361867

http://www.thestudentroom.co.uk/show....php?t=3361905
14. (Original post by Tow)
Yeah definitely.

But no question should require you to use the 'Loop' method.

Integration by parts like this is fine:
x^2sin(x)

But integration by parts of this shouldn't come up:
Sin(3x)cos(x)

Unless you can rearrange to make it so that you can integrate it with using the loop method.
I don't know the integration by loops method, what should I use to work this out?

Posted from TSR Mobile
15. (Original post by lam12)
I don't know the integration by loops method, what should I use to work this out?

Posted from TSR Mobile
Work what out?
16. (Original post by Tow)
Work what out?
The integration of the sin2x whatever it was :-)

Posted from TSR Mobile
17. (Original post by lam12)
The integration of the sin2x whatever it was :-)

Posted from TSR Mobile
I think a previous post said that you can rearrange to integrate so try that.

I can't do it right now so if you still don't understand I'll do it when I'm free.
18. do we need to know the integration of tanx cotx secx and cosecs?
19. (Original post by crepole)
do we need to know the integration of tanx cotx secx and cosecs?
They are in the formula book. You could be asked to differentiate one of the ln ones to get to tanx or something along those lines.

Posted from TSR Mobile
20. Does anyone know why you need a minus sign infront of the constant when setting up a diff. equation and its decreasing? thanks

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: April 20, 2016
Today on TSR

### Should I ask for his number?

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

Can you help? Study help unanswered threadsStudy Help rules and posting guidelinesLaTex guide for writing equations on TSR

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• 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