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

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Original post by CD223
Ew. I do not look forward to doing that. Can't believe I've forgotten if it was that bad - must have selectively blanked it :wink:


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Haha let me know how it goes. Only managed to get 62.


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Reply 621
Original post by Jimmy20002012
Haha let me know how it goes. Only managed to get 62.


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To be fair that's 98 UMS. 63 is 100 UMS.


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Reply 622
Could someone explain where I've gone wrong on June 2010 Q7?

ImageUploadedByStudent Room1432669986.797865.jpg

I've set up a quadratic in terms of α\alpha like so:

5α212α+7=05 \alpha^{2} - 12 \alpha + 7 = 0

To which the solutions are:
α=1\alpha = 1 or α=75\alpha = \frac{7}{5}

This gives co ordinates of C as:
(3,1,3)(3, -1, 3) which is correct, and (195,1,175)(\frac{19}{5}, -1, \frac{17}{5}) which is incorrect.

How can I get to the other possibility of (1,1,1)(-1, -1, 1)?


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Original post by CD223
Could someone explain where I've gone wrong on June 2010 Q7?

ImageUploadedByStudent Room1432669986.797865.jpg

I've set up a quadratic in terms of α\alpha like so:

5α212α+7=05 \alpha^{2} - 12 \alpha + 7 = 0

To which the solutions are:
α=1\alpha = 1 or α=75\alpha = \frac{7}{5}

This gives co ordinates of C as:
(3,1,3)(3, -1, 3) which is correct, and (195,1,175)(\frac{19}{5}, -1, \frac{17}{5}) which is incorrect.

How can I get to the other possibility of (1,1,1)(-1, -1, 1)?


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Not sure why it does not work using your method as I would has thought BP and AC have the same distance due to it being a parallelogram. But when I tried it the other way round of saying vector BC=AP, you get the right answer. Not too sure why you cannot do it the other way round :s.


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Reply 624
Original post by Jimmy20002012
Not sure why it does not work using your method as I would has thought BP and AC have the same distance due to it being a parallelogram. But when I tried it the other way round of saying vector BC=AP, you get the right answer. Not too sure why you cannot do it the other way round :s.


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That is odd. If anyone would be kind enough to explain why I'm sure we'd both appreciate it!


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Does anyone have any tips on how to get better at vectors? they're my only weakness on C4 and I've been trying different strategies to try and get better but it's just not happening 😭😭 any help would be really appreciated!!


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Reply 626
Original post by Bueno786
Does anyone have any tips on how to get better at vectors? they're my only weakness on C4 and I've been trying different strategies to try and get better but it's just not happening 😭😭 any help would be really appreciated!!


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What revision guide do you use? The CGP one has great tips :smile:


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ImageUploadedByStudent Room1432735618.815212.jpg Could someone please explain the working out process for this please


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Original post by CD223
What revision guide do you use? The CGP one has great tips :smile:


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I don't actually use a revision guide 😬 I'm thinking to get one, thank you!


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Reply 629
Original post by EmilyC96
ImageUploadedByStudent Room1432735618.815212.jpg Could someone please explain the working out process for this please


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ImageUploadedByStudent Room1432736371.051615.jpg

Does this help? Let me know if you need any clarification.


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Reply 630
Original post by Bueno786
I don't actually use a revision guide 😬 I'm thinking to get one, thank you!


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No problem! It does help when you get stuck :smile:


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Also how do you integrate

1 / (2rooty) dy


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Original post by CD223
ImageUploadedByStudent Room1432736371.051615.jpg

Does this help? Let me know if you need any clarification.


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Sorry I'm no good at those questions. How do you do a? I just don't understand how to make differential equations :/


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Original post by EmilyC96
Also how do you integrate

1 / (2rooty) dy


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This should help.

ImageUploadedByStudent Room1432737473.140559.jpg


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Original post by Jimmy20002012
This should help.

ImageUploadedByStudent Room1432737473.140559.jpg


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Yes!!! Thank you!!


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Reply 635
Original post by EmilyC96
Sorry I'm no good at those questions. How do you do a? I just don't understand how to make differential equations :/
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The question states that the rate of decrease of surface area AA in time tt is constant.

As the rate of change of surface area is constant, this suggests it doesn't depend on AA or tt, so they don't belong in the differential equation.

From this, we can say that, as the rate of decrease of surface area is constant,

dAdt=k\dfrac{dA}{dt} = -k

Think of it like a linear graph with a negative gradient. The gradient is constant and negative because it is a whole number and doesn't depend on the xx or yy variable.


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Original post by CD223
The question states that the rate of decrease of surface area AA in time tt is constant.

As the rate of change of surface area is constant, this suggests it doesn't depend on AA or tt, so they don't belong in the differential equation.

From this, we can say that, as the rate of decrease of surface area is constant,

dAdt=k\dfrac{dA}{dt} = -k

Think of it like a linear graph with a negative gradient. The gradient is constant and negative because it is a whole number and doesn't depend on the xx or yy variable.


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I understand! Woo 🎉 Hahaa thanks ☺️


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ImageUploadedByStudent Room1432739638.630863.jpg
From June 12 q5ai
Can someone tell me where I went wrong :/


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Reply 638
Original post by EmilyC96
ImageUploadedByStudent Room1432739638.630863.jpg
From June 12 q5ai
Can someone tell me where I went wrong :/


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ImageUploadedByStudent Room1432739906.059163.jpg


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