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# Edexcel A2 C4 Mathematics June 2015 - Official Thread watch

1. (Original post by jubilant_joej)
Sorry, I didn't mean related rates of change, I meant whats the likelihood of them giving us some information:
e.g. 'A bath is filled with hot water which is allowed to cool. The temperature of the water is theta degrees after cooling for t minutes and the temperature of the room is assumed to remain constant at 20 degrees.
Given that the rate at which the temperature of the water decreases is proportional to the difference in temperature between the water and the room.
Write down a differential equation connecting theta and t
ohhh sorry, my bad - i think i read in the spec that we will not be expected to form D.E's but I'm not entirely sure. Those examples such as yours above however should be fairly straightforward.
2. (Original post by jubilant_joej)
Sorry, I didn't mean related rates of change, I meant whats the likelihood of them giving us some information:
e.g. 'A bath is filled with hot water which is allowed to cool. The temperature of the water is theta degrees after cooling for t minutes and the temperature of the room is assumed to remain constant at 20 degrees.
Given that the rate at which the temperature of the water decreases is proportional to the difference in temperature between the water and the room.
Write down a differential equation connecting theta and t
You might be asked to? I don't know, I've been doing it in the Solomon papers. I know it's definitely a possibility in FP2 but I don't know for C4. I would just say best to have a little practice just in case though lol.
3. (Original post by Gilo98)
ohhh sorry, my bad - i think i read in the spec that we will not be expected to form D.E's but I'm not entirely sure. Those examples such as yours above however should be fairly straightforward.
Ye it didn't look too hard but I got it wrong at first. Nice one anyway
4. (Original post by Iridann)
You might be asked to? I don't know, I've been doing it in the Solomon papers. I know it's definitely a possibility in FP2 but I don't know for C4. I would just say best to have a little practice just in case though lol.
Ye going to have a look at a few questions. Cheers
5. (Original post by a.a.k)
I dont know what i am doing but i think u can implicit differentiate 3^xy.

Am i right/wrong?

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I did it this way.

Where I just used the chain rule. Differentiate the outside function, which would give and then differentiating the inside function
6. (Original post by dominicwild)
I did it this way.

Where I just used the chain rule. Differentiate the outside function, which would give and then differentiating the inside function
Yup that's what I did. Both our answers check out with Wolfram as well.

https://a086a5a2f39bda93734c56a63fab...%20Edexcel.pdf

The mark scheme has c = 1/4 (which I can't seem to get), and I've just had a look at Arsey's model answers and he has c = -1/4 but his answer at the end matches the mark scheme. Does this mean you can get a different value for c and still get the marks somehow?
8. (Original post by themorninglight)

https://a086a5a2f39bda93734c56a63fab...%20Edexcel.pdf

The mark scheme has c = 1/4 (which I can't seem to get), and I've just had a look at Arsey's model answers and he has c = -1/4 but his answer at the end matches the mark scheme. Does this mean you can get a different value for c and still get the marks somehow?
I imagine the difference comes where they've changed the sign. At some point one might have +c and the other -c, so for the first one overall it would be +1/4 and the second one would be -(-1/4), which is also 1/4. (This explanation doesn't seem to be very helpful. I suppose if you had -(b-y) = y+c, where c = -b... )

Which bit are you getting stuck on?
9. (Original post by 13 1 20 8 42)
Dunno if anyone's still interested in solving this so I'll put spoilers
Spoiler:
Show
The spec says IBP multiple times may be required; I don't think it says anything specifically about not using this kind of "loop" thing. So I feel it could feasibly come up. To be fair, once you've done the IBP twice, it should be quite obvious what to do at the end..

You can also do it by complex numbers as well if you're interested
10. Haven't started revising for this yet and have barely even learnt the course this year... Probablity of getting a b in this exam?😂🔫
11. C4 June 2014 (R) Q7b. How do I solve for 'k' - the mark scheme is very unclear
12. (Original post by curtiscowan10)
Haven't started revising for this yet and have barely even learnt the course this year... Probablity of getting a b in this exam?😂🔫
...
Attached Images

13. (Original post by Leking9)
C4 June 2014 (R) Q7b. How do I solve for 'k' - the mark scheme is very unclear
I'm assuming you divide by to so you're left with e^-k = .......
Then you just take natural logs of both sides which gives you what -k equals then just x by -1 on both sides to get k

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14. (Original post by Leking9)
C4 June 2014 (R) Q7b. How do I solve for 'k' - the mark scheme is very unclear
I'm assuming you divide by 2 so you're left with e^-k = .......
Then you just take natural logs of both sides which gives you what -k equals then just multiply by -1 on both sides to get k

Posted from TSR Mobile
15. (Original post by alibland)
I'm assuming you divide by 2 so you're left with e^-k = .......
Then you just take natural logs of both sides which gives you what -k equals then just multiply by -1 on both sides to get k

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(Original post by Leking9)
C4 June 2014 (R) Q7b. How do I solve for 'k' - the mark scheme is very unclear
any good?
Attached Images

16. (Original post by curtiscowan10)
Haven't started revising for this yet and have barely even learnt the course this year... Probablity of getting a b in this exam?😂🔫
ExamSolutions will be your best friend over the next couple of days.
17. (Original post by TeeEm)
...
What, in your opinion, is the hardest Q edexcel could throw us in C4? Horrible integration? Dodgy vector Q?
18. (Original post by Gilo98)
What, in your opinion, is the hardest Q edexcel could throw us in C4? Horrible integration? Dodgy vector Q?

The vector equation of a line is 3i -4j +5k. Find the total volume of the solid formed when it's rotated 2pi around the k axis.

(Yes, I'm joking, couldn't resist.)
19. (Original post by TeeEm)
any good?
Yeah, perfect. Thanks
20. (Original post by Leking9)
Yeah, perfect. Thanks
no worries

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