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# Edexcel C3,C4 June 2013 Thread watch

1. (Original post by Jullith)
Still need help with part c of this:

Attachment 227646

And part c of this:
(I'm confused as to what the limits are)

Attachment 227647

Help would be appreciated, thanks!
For the second one, it says the finite region of the curve bounded by x=5/2. So the limits would be 5/2 and 1 in terms of x. You need to convert them to in terms of t if you are integrating parametrically.
2. (Original post by fayled)
Change of base formula.

log10x=lnx/ln10
Didn't spot that, thank you!
3. (Original post by KD35)
Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2
Do you know the answer yourself?
4. (Original post by Giant)
For the second one, it says the finite region of the curve bounded by x=5/2. So the limits would be 5/2 and 1 in terms of x. You need to convert them to in terms of t if you are integrating parametrically.
I tried converting the limit from x to t but it didn't work for x=1, since you get t^(2)-t+1 which can't be factorised?
5. Anyone else feeling worn out just by the thought of doing this replacement paper tomorrow?
6. (Original post by Zaphod77)
Is it just the x squared, or the 2x all squared?
(Original post by fayled)
Do you know the answer yourself?
Just the x and yes I think I do
7. (Original post by Matamaticas)
Anyone else feeling worn out just by the thought of doing this replacement paper tomorrow?
Really worn out, seriously don't know what to expect. Main aim: try and get as many method marks here and there as possible.
8. (Original post by KD35)
Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2
4^(2x^2)ln(4)4x??
edit: oops, no wrong. I thought you said differentiate!
9. (Original post by KD35)
Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2
Try not to make up questions just like that, the answer has to be attainable with C4 knowledge.

http://www.wolframalpha.com/input/?i...ariable---.*--

Definitely not C4 stuff, that.
10. Can someone help me with 8b)?
So firstly I equated sin4t=0 to get x values. But I got 4 solutions? What? I didnt know what to do after... thanks

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11. (Original post by justinawe)
For 2x, yes.

In general,

are there any other uncommon one's I should know about. cause this I couldn't do I the jan 2013 and made me miss my a* by 1 mark
12. (Original post by Zaphod77)
No problem, happy to help
If its not too much to ask, do you have any tips on some stuff like integration, some of the stuff I fumble on, like substitution.

Also if you had x^3/2, For some reason I thought that would cancel down as square roots and power cancel each other, I know they do not but why?

Also on differential equations I dont know if you have done the past paper or not but june 2012 c4 q)4) It says solve the differential equation dy/dx =3/ycos^2x ... My question is the ms did not move the 3 however I did and I managed to get y^2 = 6tanx (the same answer on ms) would this be awarded the same and are there any major rules when separating differential equation ie, what you CANT do?
13. (Original post by imasha.sj)
Hey guys!

Can someone help me with Edexcel C4 review exercise question 74 (c)? I don't get why we have to integrate from 0.5 to 2....Thanks in advance
from the earlier part of the question, we find that when x=2.5 , t=0.5 and t=2. In part c we have to integrate in terms of t, not x. therefore once you intergrate using (y.dx/dt) you can simply put in the t values as the limits and get your answer! I had a confusion in this question too! But instead of using the x values, we can use the t values,either way, you will get the the region enclosed with curve.. hope this helps.
14. Anyone understand why there is different answers in question 8a june 2008???

When I sub the x value in I get t=pi/3 and when I sub the y value in I get t= pi/6
15. (Original post by KD35)
Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2
i dunno if correct but is it

4^(2(X)^2) / 4X * Ln 4?

16. why can't the cartesian equation be x = ln(root[y+2])
for part b?
y = e^2x - 2
17. (Original post by Story)
If its not too much to ask, do you have any tips on some stuff like integration, some of the stuff I fumble on, like substitution.

Also if you had x^3/2, For some reason I thought that would cancel down as square roots and power cancel each other, I know they do not but why?

Also on differential equations I dont know if you have done the past paper or not but june 2012 c4 q)4) It says solve the differential equation dy/dx =3/ycos^2x ... My question is the ms did not move the 3 however I did and I managed to get y^2 = 6tanx (the same answer on ms) would this be awarded the same and are there any major rules when separating differential equation ie, what you CANT do?
With regards to substitution, use the steps I said earlier. Never forget to change the limits, and if one substitution isn't working for you and they didn't specify the substitution you should use, try another - they'll all work out the same in the end. Only use substitution when you have a function of a function! Your second question, the power 3/2 means you square root a number and then cube it. If you had 4^3/2 you would square root it (2) and then cube it (8). If you had x^3/2 you could write it as root(x) * root(x) * root(x), which would then be the same as xroot(x) if you like With regards to your 3rd question, it doesn't matter at all. They only did it like that in the mark scheme because it involves less steps, but it doesn't matter so long as you get to the right answer Sorry about the long block of text, my enter key doesn't work on here
18. (Original post by KD35)
That is definately attainable with C4 knowledge.
The imaginary error function is covered in C4? That's news to me...
19. (Original post by sonyeric33)
i dunno if correct but is it

4^(2(X)^2) / 4X * Ln 4?
It's not C4, ignore the question.
20. (Original post by sonyeric33)
i dunno if correct but is it

4^(2(X)^2) / 4X * Ln 4?
well, thats what I guessed at first but I'm not sure if we can do it if the power isn't linear lol.

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