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# AQA Core 4 - Monday 10th June 2013 (AM) - Official Thread watch

1. Can someone help me with question 7 c) on the June 2008 C4 paper? I don't understand how you would start it.

http://filestore.aqa.org.uk/subjects...W-MS-JUN08.PDF

(It's a vector question)
2. I haven't had a proper go yet, but it strikes me that you need to write the point C as

5+ lambda
3
-3lambda

in vector form, then find AC as a vector (C - A)

you know the distance AB from the part of A,
so the magnitude of AC is just equal to that
3. (Original post by bugsuper)

5+ lambda
3
-3lambda
That's the confusing bit for me, I know this may sound weird but, isn't lambda just a constant, how is it related to C?
4. Lambda is a variable that describes the whole line.

What we're doing is saying that, because the point C is on the line, for some value of lambda, r = the point C

do you see what I mean? In this way you can write C with lambda before you know what lambda is, and then use that in your calculations
5. (Original post by Last Chance)
That's the confusing bit for me, I know this may sound weird but, isn't lambda just a constant, how is it related to C?
What lambda is telling you, is basically how far up or down you are travelling on a particular line. The bigger the value for lambda, the further away you are from the position vector. In other words, you can give a point which lies on a line a generic position vector, in terms of lambda. Once you've found how far up or down the point is (the value of lambda), you can put that back into the generic position vector and you'll be able to find the co-ordinates for C.
6. (Original post by bugsuper)
Lambda is a variable that describes the whole line.

What we're doing is saying that, because the point C is on the line, for some value of lambda, r = the point C

do you see what I mean? In this way you can write C with lambda before you know what lambda is, and then use that in your calculations
I don't understand, sorry! This stuff isn't in my book and I can't find anything online.
7. (Original post by amish123)
What lambda is telling you, is basically how far up or down you are travelling on a particular line. The bigger the value for lambda, the further away you are from the position vector. In other words, you can give a point which lies on a line a generic position vector, in terms of lambda. Once you've found how far up or down the point is (the value of lambda), you can put that back into the generic position vector and you'll be able to find the co-ordinates for C.
Sorry... I'm having trouble grasping this, I'll explain how I usually do questions

(c) The points B and C lie on l such that the distance AC is equal to the distance AB . Find
the coordinates of C. (5 marks)

What information can I obtain here is that I think?

What I've gathered

AC = root 30, calculated previously
AC = -OA + OC
B lies on the line as it's on the vector equation
C lies on the line

http://filestore.aqa.org.uk/subjects...W-QP-JUN08.PDF

I don't understand how you start
8. The person below my post explained it pretty well.

All a parametric line is is a vector on the line, and a parameter that tells you how far along the line you are.

You know that point C is on the line - so you know it's lambda * the direction vector away from that first point they give you.

You don't know how far along it is, but you can write the vector as a "general point", like I did above. Then you can use that in your calculations, along with information the question gives you, to work out what its value is.

I can't put it any simpler than that.
9. (Original post by bugsuper)

You know that point C is on the line - so you know it's lambda * the direction vector away from that first point they give you.

You don't know how far along it is, but you can write the vector as a "general point", like I did above. .
Oh okay, I understand that.

!! Was a lot simpler than I thought it would be. Thanks both.
10. (Original post by GeneralOJB)
Some hard de/vectors questions for A* peeps
Hey, thanks for these. Have you got the mark scheme?
11. Can someone help me with part bii. of this question please? I think I know how to do it but I'm not sure and the mark scheme doesn't have the answer to that part of the question on it for some reason. The paper is the Jan12 one.

(k is 72, and the equation of the tangent is "y=-16x+16" if that helps.)

12. (Original post by bornab3)
Can someone help me with part bii. of this question please? I think I know how to do it but I'm not sure and the mark scheme doesn't have the answer to that part of the question on it for some reason. The paper is the Jan12 one.

(k is 72, and the equation of the tangent is "y=-16x+16" if that helps.)

Plug x=3/2 into your y=-16x+16 to get a value for y then plug the corresponding x and y values into part a and you'll see that it equals 72 thus confirming it intersects at the x=3/2.
13. (Original post by bornab3)
Can someone help me with part bii. of this question please? I think I know how to do it but I'm not sure and the mark scheme doesn't have the answer to that part of the question on it for some reason. The paper is the Jan12 one.

(k is 72, and the equation of the tangent is "y=-16x+16" if that helps.)

14. Hi all,

Please can someone help me to understand the double angle formulae?

In class we've been taught that cos2A=cos^2A - sin^2A
and cos^2A + sin^2A=1

However, on page 5 of the AQA formula booklet, under "Hyperbolic Functions", it says: cosh^2x - sinh^2x=1
and cosh2x=cosh^2x + sinh^2x

I don't understand how both these sets of formulae are compatible? They can't both be true! What effect does "h" have on the formulae?

15. (Original post by alwayshope)
Hi all,

Please can someone help me to understand the double angle formulae?

In class we've been taught that cos2A=cos^2A - sin^2A
and cos^2A + sin^2A=1

However, on page 5 of the AQA formula booklet, under "Hyperbolic Functions", it says: cosh^2x - sinh^2x=1
and cosh2x=cosh^2x + sinh^2x

I don't understand how both these sets of formulae are compatible? They can't both be true! What effect does "h" have on the formulae?

cos/sin etc are trigonometric functions. cosh/sinh are hyperbolic functions, they're very different!

Cosh/Sinh is only used in AQA FP2. It will never come up in AQA Core 4.
16. Are any Core 4 formulae in the booklet then, or do need to memorise them? Thanks so much for the quick reply
17. Does anyone have some crazy hard stuff which may be higher level yet relevant to exam?
I know Core 4 seems to mix things up a little and it just throws whateva it can at you?

Any awesome trig stuff?
18. (Original post by LittleMissNoface)
Does anyone have some crazy hard stuff which may be higher level yet relevant to exam?
I know Core 4 seems to mix things up a little and it just throws whateva it can at you?

Any awesome trig stuff?
Have you tried the Elmwood papers? They're meant to be slightly tougher. Otherwise, you could always try a STEP I question
19. (Original post by alwayshope)
Are any Core 4 formulae in the booklet then, or do need to memorise them? Thanks so much for the quick reply
Only the following C4 identities are in the booklet:

sin(A+-B) =
cos(A+-B)=
tan(A+-B)=

Everything else you'll need to memorise, including C3 stuff.
20. (Original post by Prepotency)
Have you tried the Elmwood papers? They're meant to be slightly tougher. Otherwise, you could always try a STEP I question
Yea, STEP is a good idea!
Has anyone found any good relevant STEP questions for Core 4, coz trust me, their is gunna be that one 9 mark question which in a sentence will take like 20 minutes.

Also anyone on tips for time?
That is my killer, I never finish!!!!

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