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# Edexcel A2 C4 Mathematics June 2015 - Official Thread watch

1. (Original post by koli248)
get the directed vector AB by subtracting B from A
AB=(10i -4j +10k) you can divide by 2 so the directed vector AB equals (5i-2j+5k)
r= any point on the line + directed vector*parameter ( λ)
therefore,
r = (−3i + 3j + 2k) + λ(5i − 2j + 5k)
is it compulsory to divide it by 2
what are the formulas of like area and stuff should we know for connected rates type of questions? just want to make sure i'm fresh on my mind
Probably only need to know the area of a circle; if a cone comes up they give you the area and if a sphere, god forbid, comes up, they'll probably give that too
Cylinder I don't think they do but that's pretty obvious with the area of a circle..
3. Cones and such are given. Things that should be known are cyclinders, circles and the sort
4. (Original post by imedico10)
is it compulsory to divide it by 2
No at all
5. (Original post by imedico10)
is it compulsory to divide it by 2
nah it's just more aesthetic really; you could technically put any multiple of that vector there and it'd be correct

edit: well not zero lol
6. (Original post by tawaz1997)
Can someone please help me with Q 4b) June 2013 Replacement, I don't understand how they got 0.1 for x. Here's the paper and mark scheme...

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

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

In the question it says x<8/9 so you need to adjust the cuberoot(7100) by taking out cuberoot(1000) which gives 10cuberoot(7.1). I think there is an error in the mark scheme here as it is printed as 71 not 7.1. Then you set 8-9x = 7.1 which gives x=0.1 then sub into your expansion to get the answer
7. anyone know how to do this question? Solomon L, question 3a and 3b!
mark scheme is confusing
Attached Images

8. (Original post by Anonymous696061)
(dy/dt) / (dx/dt)

(So differentiate x & y separately, with respect to t; then divide the derivative of y over the derivative of x)

Hope this helps!
Thats differentiation.
To integrate a parametric you integrate y*(dx/dt).dt
Kind of like integrating with a substitution.
9. (Original post by ember8)
anyone know how to do this question? Solomon L, question 3a and 3b!
mark scheme is confusing
3b - factor formulae may help.

3a - Find du/dx, substitute that in and the u stuff in.
10. (Original post by Gilo98)
Yep. just stick with it and be methodical - then it really isn't that bad
I managed to get it all right except for part b which was only 1 mark lol
12. (Original post by SeanFM)
3b - factor formulae may help.

3a - Find du/dx, substitute that in and the u stuff in.
yeah done that, but i got -1/4ln2u as oppose to their -1/2lnu for 3a but no idea where i went wrong
13. (Original post by Dingdongdidly)
In the question it says x<8/9 so you need to adjust the cuberoot(7100) by taking out cuberoot(1000) which gives 10cuberoot(7.1). I think there is an error in the mark scheme here as it is printed as 71 not 7.1. Then you set 8-9x = 7.1 which gives x=0.1 then sub into your expansion to get the answer
So it's that simple, haha.Thank you!
14. (Original post by ember8)
anyone know how to do this question? Solomon L, question 3a and 3b!
mark scheme is confusing
for part a when you get ∫ x/u -1/2x du both of the x cancel out leaving you with
∫ 1/u (-1/2) du then take the -1/2 out and then integrate
15. Done all the main papers, whats best next- gold standard or the reserve, as apparently theyre quite hard.
16. (Original post by ember8)
yeah done that, but i got -1/4ln2u as oppose to their -1/2lnu for 3a but no idea where i went wrong
What did you get as dx? Did you substitute u in after substituting du in? what did you integrate overall?
17. (Original post by physicsmaths)
Yes a very wordy problem i thinkz

Posted from TSR Mobile
What do you mean by a wordy question?
18. (Original post by johnh545)
Thats differentiation.
To integrate a parametric you integrate y*(dx/dt).dt
Kind of like integrating with a substitution.
Oh crap sorry I misread that! -Thanks for correcting!!
19. (Original post by ember8)
anyone know how to do this question? Solomon L, question 3a and 3b!
mark scheme is confusing
Hopefully you can read my writing! I integrated by parts twice then replaced the last part with 9 times the original integral and then took it over to the other side.
20. (Original post by SeanFM)
What did you get as dx? Did you substitute u in after substituting du in? what did you integrate overall?
just got it! when i multiplied it by my dx/du which was -1/2(2-u)^1/2 i accidently multiplied it and then took the two out, and then wrote the 2 in again for the denominator in later working! silly mistake hahah

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