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Edexcel FP3 June 2015 - Official Thread

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Original post by 1 8 13 20 42
loci.jpg


just wondering, is it possible to rearrange for cos and sin and then sub into the identity and then use complete the square, your method looks fine i think...
Original post by Elcor
Yeah it's a silly question because you're meant to stop in (b) as soon as you get an equation, but the primal mathematician instinct in all of us wants to simplify it there and then...


But I had nowhere to stop, as soon as it turned Cartesian it was the circle equation. All I did was write x as 3costheta + 4 instead of write 2x as 6costheta + 8, I think. (see my post above with the image)
I guess I would just write for part c the same equation but with 3^2 instead of 9 as this is strictly in the general form
Original post by ninjasinpjs
just wondering, is it possible to rearrange for cos and sin and then sub into the identity and then use complete the square, your method looks fine i think...


I think that's possible, it just seems a bit long. :s-smilie:
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Original post by rachu
thank you for the questions .. they were fun to solve and look at your method of solving. I had never thought of using those addition trig identities. . I just solved them long way. Your method is faster.


thank you for the free proof reading.
I will update my site tonight
anyone have any clue about june 2014 6 c) ???
Does anyone have any tips for Further co-ordinate geometry questions on hyperbola ellipse etc, i normally lose near enough all the marks on them and manage full on the rest of the paper. Very annoying.. I just never know how to answer them!


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Original post by chughes17
Does anyone have any tips for Further co-ordinate geometry questions on hyperbola ellipse etc, i normally lose near enough all the marks on them and manage full on the rest of the paper. Very annoying.. I just never know how to answer them!


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Are there any particular parts of these questions that you struggle with/could you give an example?
What vector question is likely to come up tomorrow as I don't have time to learn all of them?
Original post by 0beany0
anyone have any clue about june 2014 6 c) ???


Just express everything in terms of the factor formulae again.
Original post by 1 8 13 20 42
Are there any particular parts of these questions that you struggle with/could you give an example?


Having looked through papers, I understand WHY they do things having looked at the mark schemes, and it seems quite obvious. but in general, it's the second part of the questions, i.e. after you've shown the equation of the tangent is..... or found whatever they've asked you. I don't really know how to explain, and I know you probably won't be able to offer any advice without examples either haha
Guys do you know why we have to normalize the eigenvectors when making the orthogonal matrix (in the process of diagonalization)? Because I've tried numerous times, and I saw on one of the MIT OCW videos the professor NOT doing that, and it still works out the same. Btw I looked at the mark scheme and apparently you HAVE to do that (it says unit eigenvectors), I just don't get why?
Original post by chughes17
Having looked through papers, I understand WHY they do things having looked at the mark schemes, and it seems quite obvious. but in general, it's the second part of the questions, i.e. after you've shown the equation of the tangent is..... or found whatever they've asked you. I don't really know how to explain, and I know you probably won't be able to offer any advice without examples either haha


Loci stuff then? Use of sin^2 + cos^2 = 1 crops up a great deal and it is often good to rearrange for costheta and sintheta in terms of x and y and then you can square both terms and it must sum to 1, thus eliminating the trig. Even if this identity can't be used the principle point is just rearranging to eliminate theta.
Original post by 1 8 13 20 42
Loci stuff then? Use of sin^2 + cos^2 = 1 crops up a great deal and it is often good to rearrange for costheta and sintheta in terms of x and y and then you can square both terms and it must sum to 1, thus eliminating the trig. Even if this identity can't be used the principle point is just rearranging to eliminate theta.


thank you, this will help quite a bit as before I was just going off natural instinct, rather than having anything to look out for. could you help me with the definitions of co-ordinate geometry? I know we wont be asked them, but I am hopeless at remembering words, so have never even remembered what foci, directrices, eccentricity etc even mean...
Original post by gagafacea1
Guys do you know why we have to normalize the eigenvectors when making the orthogonal matrix (in the process of diagonalization)? Because I've tried numerous times, and I saw on one of the MIT OCW videos the professor NOT doing that, and it still works out the same. Btw I looked at the mark scheme and apparently you HAVE to do that (it says unit eigenvectors), I just don't get why?


you might have to watch the video more carefully, he might of done something and did not say he done it
Original post by chughes17
thank you, this will help quite a bit as before I was just going off natural instinct, rather than having anything to look out for. could you help me with the definitions of co-ordinate geometry? I know we wont be asked them, but I am hopeless at remembering words, so have never even remembered what foci, directrices, eccentricity etc even mean...


I only know how to describe the foci and directrices mathematically, I am not quite sure why they are chosen in the manner they are. Their equations for a general hyperbola/ellipse are given in the formula booklet. With foci, there are always two (symmetric) foci for ellipses and hyperbolas, while there is just one for a parabola (there is a big table showing all this in the booklet). A focus is just a point. In contrast a directrix is a line; once again we have two directrices for all but parabolas.
The eccentricity is something I perhaps can explain in a more specific sense, this is the ratio (PS/PM), where P is a general point on the conic (all of the graphs we do being conics), S is one if its foci and M is the corresponding directrix (you always have one positive and one negative directrix and the same for foci, positives correspond with positives and - with - naturally)
For ellipses, 0 < PS/PM < 1, i.e. 0 < e < 1. That is to say that the distance to the directrix from any given point is always greater than the distance to the focus. For parabolas, their defining point is rather PS = PM. For hyperbolas, you have 1 > PS/PM; the distance to the focus from a point is always greater than the distance to the directrix.
Any one happen to know if we must memorise the substituions used in integration in chapter 4?


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Could someone help me with 2b and 2c
Original post by ninjasinpjs
you might have to watch the video more carefully, he might of done something and did not say he done it


I checked myself multiple times. And yeah I'm pretty sure he never said anything about normalizing the vectors. Also see..
Capture d’écran 2015-06-21 à 13.09.01.png
Original post by nayilgervinho


Did you do 2a, well if you have, do the same with the quadratics in 2b and c.

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