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# AQA A2 Mathematics MPC4 Core 4 - 9th June 2015 [Discussion & unofficial markscheme] watch

1. (Original post by ubisoft)
There was nothing wrong with the exam questions. They were all within the specification. If you thought they were difficult, then grade boundaries should reflect that.

It's good they're making it difficult anyway. Too many people who are not even good at maths are getting A*s.
I agree there was nothing wrong with the questions. I think they were harder than usual but there was nothing to catch people out purposely or anything. Only thing I'd say is the integrating tan was a bit strange, maths teachers told me we'd never have to know it or use it. I figured it out in the exam but I do think it was a bit odd, but still within the spec. Don't agree about people who get A*s 'not being good at maths' though. Pretty sure anyone who either has the natural ability, or has worked hard enough to get an A* is considered decent at maths (at this level of course). Also what you said about the grade boundaries reflecting the difficulty is so true, more people need to realise this instead of making petitions and stuff to decrease them 😂
2. (Original post by chococup123)
Can anyone explain to me the answer for question 7 june 2013 paper please?

The height of the tide in a certain harbour is h metres at time hours. Successive high tides occur every 12 hours.
The rate change of the height of the tide can be modelled by a function of the form acos(kt), where a and k are constants. The largest value of this rate of change is 1.3 metres per hour.

Write down a differential equation in the variables h and t. State the values of the constants a and k.
I have given an in-depth explanation a few pages previous, let me go find it for you .
3. (Original post by ubisoft)
That is absurd lmao. Sorry I don't have to work too hard in maths to get a good grade. Maybe I should fail on purpose because I didn't work hard enough.

If people have a talent in maths, why shouldn't they use it?
yeah i understand, those who are good at maths naturally but also worked hard to obtain these grades should be rewarded equally.
When you talked about A* students struggling, i think step papers are designed so that you don't just 'pass an exam' as well.
4. (Original post by chococup123)
Can anyone explain to me the answer for question 7 june 2013 paper please?

The height of the tide in a certain harbour is h metres at time hours. Successive high tides occur every 12 hours.
The rate change of the height of the tide can be modelled by a function of the form acos(kt), where a and k are constants. The largest value of this rate of change is 1.3 metres per hour.

Write down a differential equation in the variables h and t. State the values of the constants a and k.
Excellent description from datpr0 earlier in the thread:

Basically it's modelling the change in height of the tide over a period of time (i.e. rate of change of the height of the tide) as a cosine graph, whereby the maximum and minimum values for this are 1.3 and -1.3 (dh/dt = +/- 1.3).

From the question you know: dh/dt = acos(kt).

From a cosine graph you know that the maximum and minimum points occur at 1 and -1 respectively (i.e. cos = 1 or -1). Therefore a = 1.3 or -1.3. You can consider this as a stretch parallel to the y-axis of SF 1.3 if you like.

k is adjacent to the t in the model and t is being measured on the x-axis. You know the period of a cosine graph is 2pi and the tides occur every 12 hours (i.e. t = 12). This means that k becomes 2pi/12 in order to cancel with the 12 introduced through t so that you end up with cos(2pi) not cos(12).
5. (Original post by datpr0)
Hey, don't frown upon me ... I'm just good at maths!
And I do revision! Just less than others! Because I have a good memory! It's not my fault!
Don't frown upon me !
Its not you dont worry
6. good luck tomorrow everyone
7. (Original post by chococup123)
Can anyone explain to me the answer for question 7 june 2013 paper please?

The height of the tide in a certain harbour is h metres at time hours. Successive high tides occur every 12 hours.
The rate change of the height of the tide can be modelled by a function of the form acos(kt), where a and k are constants. The largest value of this rate of change is 1.3 metres per hour.

Write down a differential equation in the variables h and t. State the values of the constants a and k.
Sorry if it's a mess. Just reply if there's anything you don't understand 😁
8. (Original post by RhyaCeri)
good luck tomorrow everyone
Thanks a lot!
Good luck to you too .
9. Alright I'm going to redo the June 2014 as my final bit of revision in a bit but until then does anyone have some tricky vectors questions suggestions (if not vectors then differential equations, and if not differential equations then just any nasty C4 questions)?
10. (Original post by 2014_GCSE)
Excellent description from datpr0 earlier in the thread:

Basically it's modelling the change in height of the tide over a period of time (i.e. rate of change of the height of the tide) as a cosine graph, whereby the maximum and minimum values for this are 1.3 and -1.3 (dh/dt = +/- 1.3).

From the question you know: dh/dt = acos(kt).

From a cosine graph you know that the maximum and minimum points occur at 1 and -1 respectively (i.e. cos = 1 or -1). Therefore a = 1.3 or -1.3. You can consider this as a stretch parallel to the y-axis of SF 1.3 if you like.

k is adjacent to the t in the model and t is being measured on the x-axis. You know the period of a cosine graph is 2pi and the tides occur every 12 hours (i.e. t = 12). This means that k becomes 2pi/12 in order to cancel with the 12 introduced through t so that you end up with cos(2pi) not cos(12).
oh wow thank you so much, that is very helpful
11. Any hard c4 paper suggestion?
12. (Original post by yasmin221b)
On Q8bii January 2011, how do you know which 'p' to sub in to get your coordinates. Because I used p=1 instead of p=5/7 and therefore didn't get the right coordinates, so I was wondering how you're meant to work out which one is correct?
I commented earlier on this on this post. It is a trapezium, therefore you need to smaller value because if you use the larger value, the shape will be a parallelogram. (As the lengths will be the same CD, i believe, but the shape wrong). If you still don't understand let me know and I will draw a diagram.
13. (Original post by JackNorman)

Sorry if it's a mess. Just reply if there's anything you don't understand 😁
I get it now, thank you so much
14. (Original post by hamza3256)
Any hard c4 paper suggestion?
Jan 13 is the hardest apparently.
15. Right so for this question I have my workings, don't still seem to know how to get n=-2k??

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16. (Original post by Jimmy20002012)
Right so for this question I have my workings, don't still seem to know how to get n=-2k??

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It's literally a matter of comparing coefficients. The binomial expansion given in b (6x2 + px3 + ...) starts at the term x2 which means that the coefficient of x in the expansion must have been 0. Therefore -2k - n = 0, => n = -2k.
17. (Original post by datpr0)
It's literally a matter of comparing coefficients. The binomial expansion given in b (6x2 + px3 + ...) starts at the term x2 which means that the coefficient of x in the expansion must have been 0. Therefore -2k - n = 0, => n = -2k.
Wow how did I not notice that! Thanks. How you feeling for C4?

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18. (Original post by Jimmy20002012)
Wow how did I not notice that! Thanks. How you feeling for C4?

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Confident on everything except vectors (the standard stuff I can do easily) . My vectors has exponentially improved since Friday but it still takes me too long to figure out the tricky final part of a vectors question. I guess, overall, though pretty good !
19. Guys urm any tips on how to tackle vector questions like the ones where it talks about area or about triangle and square trapezium and stuff. I'm really stuck on those 😑
20. (Original post by Leeki)
Guys urm any tips on how to tackle vector questions like the ones where it talks about area or about triangle and square trapezium and stuff. I'm really stuck on those 😑
Best advice is to draw and diagram and just list everything you know. Approach it like solving a puzzle, if you like, lay out all the pieces in front of you; consider what you need to find/produce and what you have; apply some of the standard vectors principles to the puzzle and you'll likely see how to get to the answer.

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