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# Edexcel A2 C4 Mathematics June 2015 - Official Thread watch

1. (Original post by Oxyfrost)
Hello, can someone help me? Either I'm very confused, or Solomon papers have got the mark scheme wrong. Paper A, Question 5. Trapezium rule. Equation is 4(x^0.5)(e^-x).
My value for x=2 is 0.766 (3sf), but on the mark scheme it says 1.083. Can someone please help me to understand this discrepancy? All my other values are correct.

Question and mark scheme attached.
Please can anyone help me with this question?
2. (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..

I did the integration by parts twice, but I end up needing to integrate the original problem, what's the trick?
3. I dont know what i am doing but i think u can implicit differentiate 3^xy.

Am i right/wrong?

Posted from TSR Mobile
Attached Images

4. (Original post by Oxyfrost)
Please can anyone help me with this question?
I got the same value as you when I tried...
5. (Original post by somevirtualguy)
I did the integration by parts twice, but I end up needing to integrate the original problem, what's the trick?
What would you do if that original integral was just any old variable?
Spoiler:
Show
Assuming you got the negative of the original integral on the RHS, move this over to the LHS, then dividing will give the integral

6. (Original post by somevirtualguy)
I got the same value as you when I tried...
Maybe the mark scheme is incorrect then. That would be a relief. Scary when you get something so easy wrong this close to the exam :P
7. (Original post by 13 1 20 8 42)
What would you do if that original integral was just any old variable?
Spoiler:
Show
Assuming you got the negative of the original integral on the RHS, move this over to the LHS, then dividing will give the integral

Sorry I don't follow, I've never really seen this way...
8. For those 1 marker type questions in binomial expansions, where they ask for the set of values of x for which your expansion is valid, what if you're adding two different expansions together?

What would the set of values be?
9. (Original post by 13 1 20 8 42)
What would you do if that original integral was just any old variable?
Spoiler:
Show
Assuming you got the negative of the original integral on the RHS, move this over to the LHS, then dividing will give the integral

Ignore me I've just done it, it feels like really dodgy maths haha but it makes sense thanks for the help
10. Guys is there any 1/2 marker worded answers we should know for C4? For example in the C3 paper there was that one about it being a many to one function.

Another example would be in C4 when you have to say if the trapezium rule has overestimated or underestimated the area, and you say whether the trapezia lie above or below the curve
11. (Original post by nbofni)
For those 1 marker type questions in binomial expansions, where they ask for the set of values of x for which your expansion is valid, what if you're adding two different expansions together?

What would the set of values be?
Whichever restriction is tighter
For instance if one is |x| < 8/9 and another is |x| < 1/4, both must hold, but if |x| < 1/4, then |x| < 8/9 anyway
12. (Original post by anonwinner)
Guys is there any 1/2 marker worded answers we should know for C4? For example in the C3 paper there was that one about it being a many to one function.

Another example would be in C4 when you have to say if the trapezium rule has overestimated or underestimated the area, and you say whether the trapezia lie above or below the curve
think thats all you need
13. anyone has any hard set of integration questions, that the topic that i think Edexcel will try to ''ra pe'' us with
14. (Original post by anonwinner)
Guys is there any 1/2 marker worded answers we should know for C4? For example in the C3 paper there was that one about it being a many to one function.

Another example would be in C4 when you have to say if the trapezium rule has overestimated or underestimated the area, and you say whether the trapezia lie above or below the curve
The other would be in differential equations, where you have to say what certain variables represent.
Or I was doing a Solomon paper today and you had to comment on the sustainability of a mathematical.
model
Wouldn't get two worked up on 1/2 markers though as it's completely dependent on the question.
15. Oh gosh, how am I going to get 90, given the amount of silly errors I make
16. How likely is it we'll be asked to form a differential equation from some information? And any tips on doing this?
17. (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?

Posted from TSR Mobile
I had a go, not sure if it's right. Your working doesn't seem to have any implicit differentiation in it?
Apologies for poor lighting. Why are you trying to implicitly differentiate that?

EDIT: My bad just realised I forgot to multiply out the bracket fully.
Attached Images

18. (Original post by jubilant_joej)
How likely is it we'll be asked to form a differential equation from some information? And any tips on doing this?
kind of likely. the Qs are very similar though. give you a formula. give the rate of change of 1 of the variables in formula and want you to find the rate of change of the other variable in the formula at some value. always end up differentiating the formula and diving this derivative by the rate of change they give you before subbing in the value they want the rate of change at.
19. (Original post by Gilo98)
kind of likely. the Qs are very similar though. give you a formula. give the rate of change of 1 of the variables in formula and want you to find the rate of change of the other variable in the formula at some value. always end up differentiating the formula and diving this derivative by the rate of change they give you before subbing in the value they want the rate of change at.
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
20. (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?

Posted from TSR Mobile
(Original post by veggienator)
That'll be great
(Original post by TheAnnabelle)
Hmm....I'm not sure...I'll see if I can ask a teacher tomorrow and get back to you guys

The result is the bit in the middle surrounded by scribbles, and ignore the equating to 0. I just do that without thinking :P

Also if you want to check your answer you can use Wolfram Alpha: http://www.wolframalpha.com/input/?i...%28xy%29+wrt+x

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