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# Edexcel A2 C4 Mathematics June 2015 - Official Thread watch

1. (Original post by manlikem)
thanks! and if I use substitution could I make cos x = u?
See my post above.
2. Think ive got an answer!!
cos^4x --> integrate this --> -4sinxcos^3x
You want sinxcos^3x, so just divide by 4 to give -1/4cos^4x+c

Hope this helps!!
3. (Original post by raypalmer)
Hopefully vectors aint the last question, when it is its usually a mad ting

Posted from TSR Mobile
I can't do any of c4 apart from vectors at the moment lol
too many exams in a row
4. (Original post by Paraphilos)
See my post above.
the question is

If I want to solve this q. by substitution can I make cosx = u?
5. (Original post by MrBowcat)
So what what would you do exactly after you get cosx - cosx sin^2x ??
Integral of cosx sin^nx dx
= (1/n+1)sin^(n+1)x + c
This is something you are expected to be able to recognise in an exam.

I could do the question on paper if you like?
6. (Original post by frozo123)
I can't do any of c4 apart from vectors at the moment lol
too many exams in a row
same here! learning integration now and after that need to go through all vector questions and differential equations
7. (Original post by frozo123)
is it y=2(e^tan3x+1)?
That is not what I got from the brief calculations I just did; you should initially arrive at:

From there, can you see where to go?
8. (Original post by manlikem)
the question is

If I want to solve this q. by substitution can I make cosx = u?
yes you can
9. (Original post by manlikem)
thanks! and if I use substitution could I make cos x = u?
That is exactly what you should do, in my opinion. At least, that is a systematic method; as one poster has stated above, there are general formulae for the integration of functions which are comprised of both sine and cosine functions but you can do it from first principles in the exam by using a suitable substitution. The general formulae for each case is derived in the same way.
10. (Original post by sj97)
Can you please explain how to do part b to me? ANd hwo do you get that x = 0.1?
https://a086a5a2f39bda93734c56a63fab...%20Edexcel.pdf
number 4
took me a while to figure it out...at first I just substituted normally but the x value i got was -788 which was wayyyyy tooo big so I knew it was wrong...

its 0.1 because you see the limits they give you, its x<8/9
therefore you have to convert 7100 into 7.1 before you can solve to find x...

I can't really draw it on here...
ummm

(7100)^1/3 = (1000)^1/3 (7.1)^1/3 = 10(7.1)^1/3
then you can do 8-9x = 7.1
x = 0.1

then the rest is just standard

sorry it took me a while... I was doing part a as well
11. (Original post by sincostanxxx)
Can anyone explain question 8F from the IAL January 2014 paper (link: http://www.physicsandmathstutor.com/...rs/c4-edexcel/ )
Thank you ^.^
Draw it. Basically find AX, and find the general vector from X to a point on line2 (line2 general vector minus X). Find when this vector magnitude is equal to the AX magnitude you found. This should give you 2 parameter values, which you sub in to get b1 and b2.
12. (Original post by frozo123)
I got an idea for you
stand 2m away from your wall
step 1
Walk forward ( perpendicular ) until your hand bangs against the wall

after that
Stand in the exact same spot, but try touching the wall at the end of the room

which one took less less time and distance?
Loool good thing i put my hand there or i would've been knocked out for the exam tomorrow

Thanks
13. (Original post by Paraphilos)
That is not what I got from the brief calculations I just did; you should initially arrive at:

From there, can you see where to go?
ye I did that I and got lny=tan3x+ c
so c= ln2 +1

then I rearranged it, what have I done wrong?
edit: actually wait
is it tanx?
14. (Original post by arsenalfc97)
Loool good thing i put my hand there or i would've been knocked out for the exam tomorrow

Thanks
My teacher explained it like that but with heads banging and seems like our class remembers it lol
15. (Original post by mb_12)
Integral of cosx sin^nx dx
= (1/n+1)sin^(n+1)x + c
This is something you are expected to be able to recognise in an exam.

I could do the question on paper if you like?
Yes please, would greatly appreciate that!
16. (Original post by Paraphilos)
That is exactly what you should do, in my opinion. At least, that is a systematic method; as one poster has stated above, there are general formulae for the integration of functions which are comprised of both sine and cosine functions but you can do it from first principles in the exam by using a suitable substitution. The general formulae for each case is derived in the same way.
thanks! because on the mark scheme it says that I have to make sinx= u. But I in an exam I would have made cosx = u so I was confused. Does it matter which value you make u ?
17. (Original post by frozo123)
ye I did that I and got lny=tan3x+ c
so c= ln2 +1

then I rearranged it, what have I done wrong?
edit: actually wait
is it tanx?
First, note that the LHS consists of rather than ; and yes, the integral of that function on the RHS is
18. (Original post by Maham88)
yes you can
thaaanks!
because in the mark scheme they made sinx= u and not cosx =u so I was confused
19. (Original post by MrBowcat)
So what what would you do exactly after you get cosx - cosx sin^2x ??
Reverse chain rule, for sin^3x. That would turn out to be sinx- 1/3sin^3x.
20. (Original post by Paraphilos)
First, note that the LHS consists of rather than ; and yes, the integral of that function on the RHS is
omg I'm freaking out I can't integrate
so if there's a coefficient in a trig function you keep it
but if the angle is say k
you do 1/k times the coefficient and integration of the trig function right?

y=2(e^3tanx-3 ) ?

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