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OCR MEI C4 - June 13th 2011

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Reply 20
Original post by Junwin
But if you want to get the cartesian equation for the plane you need d which is a.n? So I reckon you need to know how to work out d, but it's just the dot product of a position vector of a point on the plane and the normal.


Oh yer I completely agree but I meant I don't think you need to know in detail how to derive that formula, but yes I agree you do have to know the formula and how to apply it
How do you work out the cartesian equation of a plane?
Reply 22
can anyone help me with q6i) on the june 2006 paper...

http://www.mei.org.uk/files/papers/c406ju_83nd.pdf

I don't understand why at E, theta = 2pi :frown:
Original post by dolmio
can anyone help me with q6i) on the june 2006 paper...

http://www.mei.org.uk/files/papers/c406ju_83nd.pdf

I don't understand why at E, theta = 2pi :frown:


Its a curve that goes from 0 to 2pi as stated.
Reply 24
Original post by dolmio
can anyone help me with q6i) on the june 2006 paper...

http://www.mei.org.uk/files/papers/c406ju_83nd.pdf

I don't understand why at E, theta = 2pi :frown:


As E is on the x axis, make y=0, so cos(theta)=1.
Reply 25
Original post by Oh my Ms. Coffey
Its a curve that goes from 0 to 2pi as stated.


FML, didn't read that.

In part 2, I don't see how they differentiate y - as a is a constant surely the derivative of it is just a, so it should be a + asintheta?
Reply 26
Hi! I don't really know what to think of this paper!
I'm feeling pretty confident about the actual C4 paper in general. Personally hoping for some vectors, but not too complicated.
I can never get those little 3 mark trig questions either, when they say show 'this' = 'that', so I'm hoping that doesn't come up!
I'm really worried about the comprehension paper though. :frown: I've done about 5 now, and some are fine, but others I completely crash out on. I suppose it just depends on the topic in hand, and whether I understand it. I can definitely see myself using the whole hour to do it though, just in case. :biggrin:
Original post by dolmio
FML, didn't read that.

In part 2, I don't see how they differentiate y - as a is a constant surely the derivative of it is just a, so it should be a + asintheta?


Try product rule, the a will differentiate to 0.
Reply 28
Original post by dolmio
FML, didn't read that.

In part 2, I don't see how they differentiate y - as a is a constant surely the derivative of it is just a, so it should be a + asintheta?


Derivative of a constant is 0...
Reply 29
Original post by Oh my Ms. Coffey
How do you work out the cartesian equation of a plane?


You'll often be given the normal to the plane, so say that this normal you are given is n=(a, b, c)

You'll also be given a point on the plane (or one that you've worked out) so say that this is a=(p, q, r)

You need to work out what a.n is - call this d.

Then its as simple as writing your equation in the form: ax+by+cz-d=0
Notice that its MINUS d, not plus d :smile:

Original post by Oh my Ms. Coffey
Theres just so many new terms, I can do easy questions but fall for mistakes like working out an angle when its like a minus vector you've got to use (giving you an obtuse angle) where I would use the vector in a +ve direction and get a small angle out.


Yeah, thats an easy one to do. I never notice until I get the obtuse angle, then realise I've got a wierd answer and I should have done it the other way round and have to go back and do it again.


Original post by ben10
if you had to work out a cartesian equation of a plane you would need d. which is a dot n ..
do we need to know how to derive d = a dot n
cuz we went through a long method on how to derive it .. unsure weaher it was just to gain a clearer understanding.


I think it was just to gain a clearer understanding. You just need to know that d=a.n and I've never come across anything that asks WHY you have to do that...
can't really think of anything thats stupidly hard....I just keep on making amateur mistakes (not reading the full question, signs etc)


The comprehension is a bitch though!
Original post by twelve
You'll often be given the normal to the plane, so say that this normal you are given is n=(a, b, c)

You'll also be given a point on the plane (or one that you've worked out) so say that this is a=(p, q, r)

You need to work out what a.n is - call this d.

Then its as simple as writing your equation in the form: ax+by+cz-d=0
Notice that its MINUS d, not plus d :smile:



Yeah, thats an easy one to do. I never notice until I get the obtuse angle, then realise I've got a wierd answer and I should have done it the other way round and have to go back and do it again.





I think it was just to gain a clearer understanding. You just need to know that d=a.n and I've never come across anything that asks WHY you have to do that...


So d is the normal to the plane, eg of plane x+2y+3z would be 1,2,3 product ruled by a position vector.
Didn't lose a single mark on section A in Jan and just flopped section B and the comprehension. Working hard through section B's now... fingers crossed!
Reply 33
Original post by Oh my Ms. Coffey
So d is the normal to the plane, eg of plane x+2y+3z would be 1,2,3 product ruled by a position vector.


n is the normal to the plane, and d is a.n - where a is any point on the plane, and n is the normal to the plane. In the example you gave, 1,2,3 is the normal to the plane.
Original post by twelve
n is the normal to the plane, and d is a.n - where a is any point on the plane, and n is the normal to the plane. In the example you gave, 1,2,3 is the normal to the plane.


thankyou, I shall make a poster out of this (LV)
Reply 35
Original post by Zagreus_92
Oh yer I completely agree but I meant I don't think you need to know in detail how to derive that formula, but yes I agree you do have to know the formula and how to apply it


Oh righttttttttttttttttttttttttttt, I get ya :smile:
Not too worried about this. Maybe about the comprehension paper, though.
Reply 37
any tips for the comprehension paper

i dont get this damn thing at all :frown:
Reply 38
Original post by kalok
any tips for the comprehension paper

i dont get this damn thing at all :frown:


I know me neither. I just don't know how to explain any of it. On pretty much every two mark question I only get 1 mark :/
Reply 39
has anyone got the jan 11 C4 paper + ms please?

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