[Waqar.]

how do we know when to multiply dy by dt/dy? I've seen it a few times but I always forget when i need to do that, is it when I change the limits?

[happ]

when you guys integrate using substitution do you do it in sections or do everything at the same time?

[exe]

(Original post by This Honest)
Thanks!!!

When you're adding and substracting logs, must the number be the same?

As in I can't do ln4 -0.5ln2 straight away, I have to make sure both terms are in ln2?

if you have to make it a single log, the question will explicitly state it

[This Honest]

(Original post by James A)
ok,

so you get

∫(x/x+1)dx

u = x + 1

therefore x = u - 1

dx/du = 1

du = dx

hence replacing the integral with this info

∫(u-1)/u . du

∫(u/u)-(1/u) . du

∫ 1 - (1/u) . du

= u - ln(u) + C

I did that look above
But when I added my limits 0 and 3 I don't get what the MS says
Solomon paper E last question

[CraziiFreak]

(Original post by King_Arthur)
I love maths but it's still sickening and we had and M4 paper right at the beginning which was just impossible (actually impossible other than a few parts ) breaks down the moral stupid edexcel

Ahhh that sucks but dont worry you probably did finee.
damn.. i understand.

[Dixie]

how do you know when to use substitution? like i only use it when they say, 'using the sub x= ...'

[stuck18]

(Original post by excell)
Rates of change will probably come up now it wasn't in January

thats exactly what im thinking. I hope its not the end question.. cos it if its in the middle somewhere.. its not that bad.. Ahhhhhhh, i'm SO SO SO SO SO SCARED !!

[chill543]

(Original post by Mike-nificent)
emmm i don't really understand how to implicitly differentiate 3x²y


anyone??

product rule
bit like in c3 if we had (4x)sin(x)
so 3x^2(y)
= 6xy + 3x^2(dy/dx)
evertime you iff something with y you get dy/dx

hope that helps?

[.Missy]

(Original post by excell)
Use the product rule.

u = 3x^2
v= y

(Original post by A128)
U gotta use the product rule so:

3x^2 dy/dx + 6xy

Why is the dy/dx on the x part. Not the y

[CrimsonArc]

(Original post by exe)
not me..

im gonna relax today. gonna do 4 papers chilledly and then try and relax for tomorrow... once you know all the techniques it's all about good sleep and retaining focus and getting into the right mindset

Totally agree with you (y) :d !

[SmithytheDrummer]

(Original post by CraziiFreak)
Yeahh i think so too. Not good
but still..

It sort of did come up in Jan 2012 for the last question though...

[Mike-nificent]

http://www.thomas-reddington.com/upl...p_jan_2012.pdf
can anyone explain how to do 3 b and c

[chill543]

(Original post by Dixie)
how do you know when to use substitution? like i only use it when they say, 'using the sub x= ...'

when you can solve it using the usaul methods

e.g you cant use the integration rule vdu = vu - ing(udv)
on ((sin^2)x)cosx
so you would have to use the subsition method
hope taht helps

[godknows]

(Original post by Mike-nificent)
http://www.thomas-reddington.com/upl...p_jan_2012.pdf
can anyone explain how to do 3 b and c

http://www.youtube.com/watch?v=mOsFrYJh8vA

[Akbar2k7]

(Original post by .Missy)
I dont get why we put the dy/dx on the 3x^2. Thought it was just on Y

Cause you differentiate y to make dy/dx and multiply it by the undifferentiated 3x^2 Product rule .

[arvin_infinity]

(Original post by Elle_6)
YOu cant integrate ln(x) like that you have to do 1 x ln(x) and do integration by parts.
The differentiation is correct though

So that will be xlnx-∫..
right?

[Gman1234]

What there be times where you have to make up your own substitution or would you always be provided it?

[James A]

(Original post by This Honest)
I did that look above
But when I added my limits 0 and 3 I don't get what the MS says
Solomon paper E last question

just to confirm with you, was 3 the upper limit, right? and 0 being the lower limit?

[chill543]

(Original post by Mike-nificent)
http://www.thomas-reddington.com/upl...p_jan_2012.pdf
can anyone explain how to do 3 b and c

comparing cooefficeint
mutiply it all out
so 2(you expansion)+kx(your expansion) = the thing it says
compare coefficeints of x
so kx=7/4
you will get something like that

[exe]

(Original post by 101101)
Why did this have to be an afternoon exam. ***** ********

agreed .... hate sitting with my thumb up my arse waiting to start the party