Year 12s: what will be the first way you research your future options? >>

Edexcel C3,C4 June 2013 Thread

Scroll to see replies

Okay jan 2013 help!!!!

Question c)

Would like if someone can explain through worked solution preferable a picture of your working! ImageUploadedByStudent Room1371309749.205103.jpg

ImageUploadedByStudent Room1371309749.205103.jpg

Posted from TSR Mobile

Reply 3621

Econ1994

how would people integrate 1) x/x-2 and 2) x/2-x
?

Reply 3622

nukethemaly

I made these for C2, but they're still relevant to C4, so here are the formulas for shapes etc, and the log rules

Sorry its a bit all over the place but hope it helps!

Today can we all use this thread with productive revision! No more dwelling on Thursday! Lets murk c4 by helping each other out let's crank up our revsion with the question I posted previously lol

On a serious note need help on that question!!! Jan 13 paper look at the pic I posted earlier!!!

Posted from TSR Mobile

Reply 3624

nukethemaly

Original post by orange94

Okay jan 2013 help!!!!

Question c)

Would like if someone can explain through worked solution preferable a picture of your working! ImageUploadedByStudent Room1371309749.205103.jpg

Posted from TSR Mobile

Sure let me grab some paper

Reply 3625

nukethemaly

Original post by orange94

Okay jan 2013 help!!!!

Question c)

Would like if someone can explain through worked solution preferable a picture of your working! ImageUploadedByStudent Room1371309749.205103.jpg

Posted from TSR Mobile

Here you are, sorry its a bit messy. let me know if you don't understand something

photo (34).JPG241.0KB

Reply 3626

justinawe

Original post by nukethemaly

I made these for C2, but they're still relevant to C4, so here are the formulas for shapes etc, and the log rules

Sorry its a bit all over the place but hope it helps!

so jelly of that handwriting :zomg:

Reply 3627

nukethemaly

Original post by justinawe

so jelly of that handwriting :zomg:

I cant keep it up during exams though hahaha

Reply 3628

justinawe

Original post by nukethemaly

I cant keep it up during exams though hahaha

Who can?

My handwriting is meh as it is... during exams it's probably illegible :s-smilie:

Reply 3629

madaboutmambo

Original post by Econ1994

how would people integrate 1) x/x-2 and 2) x/2-x
?

HI Im not too sure either but I think it's by substitution.

take u = x - 2
so that du/dx = 1 meaning du = dx
and also note that x = u + 2

the question can then be written as (u+2)/u so that you have to integrate 1 and (2/u)
this gives u + 2 ln (x - 2 )

subtitution u = x - 2 gives

x - 2 + 2 ln (x - 2 ) + c

^ please check if the answer is right. If it is, use a similar method to solve part b
Hope this helps

Reply 3630

nukethemaly

Original post by Econ1994

how would people integrate 1) x/x-2 and 2) x/2-x
?

Here you are!

053.JPG215.7KB

Reply 3631

nukethemaly

Original post by justinawe

Who can?

My handwriting is meh as it is... during exams it's probably illegible :s-smilie:

I read examiner reports for biology sometimes and my god, you should see a few of the students on there. They still score full marks surprisingly. It must be tough being an examiner.

Reply 3632

AS01

Original post by Econ1994

how would people integrate 1) x/x-2 and 2) x/2-x
?

substitution
u=x-2 so du/dx= 1 du=dx
x=u+2
so u integrate u+2/u = 1+2/u
which is u + 2ln|u|+c

Reply 3633

justinawe

Original post by nukethemaly

I read examiner reports for biology sometimes and my god, you should see a few of the students on there. They still score full marks surprisingly. It must be tough being an examiner.

It probably is. Some people have bad enough handwriting as it is, who knows what kinds of abominations are churned out in exams?

Reply 3634

Revisionbug

so is anyone changing their c4 prep i am im going to do less papers and more questions from the book as the book has sooooooo many questions that book was key for my m1 i think topic based studying is better for maths than just doing loads of past papers also the book questions are harder then the papers but im kind of scared of C4 the pressure was high for C3 and a little change in style distorted me i hope il keep it together for C4 :frown:

Reply 3635

justinawe

Original post by Econ1994

how would people integrate 1) x/x-2 and 2) x/2-x
?

An alternate method (instead of substitution) would be to just split it into partial fractions. Which in this case would probably be simpler and faster than substitution, though both methods should be pretty quick.

\displaystyle \int \frac{x}{x-2} \ dx

= \displaystyle \int \frac{x-2+2}{x-2} \ dx

= \displaystyle \int \left( \frac{x-2}{x-2} + \frac{2}{x-2} \right) \ dx

= \displaystyle \int \left( 1 + \frac{2}{x-2} \right) \ dx

= x + 2\ln (x-2) + C

Noting that

\dfrac{x}{2-x} = - \dfrac{x}{x-2}

, you should be able to do part b the same way.

Reply 3636

Poffertje

Hey, could someone please explain Q20 from Review exercise C4 book. I'm not sure how you would get a.b from the info given! Thanks :smile:

Reply 3637

Tanomc

Since people are helping, might as well ask for help.

HOW DO YOU DO (a) ?

Thanks :smile:

Reply 3638

tc1993

Original post by Econ1994

how would people integrate 1) x/x-2 and 2) x/2-x
?

Original post by Econ1994

how would people integrate 1) x/x-2 and 2) x/2-x
?

In this case I firstly make the substitution of u = x-2 therefore du = dx
So because u = x -2 then x = u + 2 so the new equation is

u+2/u du the next step is to split the fraction into 2

u/u + 2/u now because du = dx you can integrate with respect to x giving

1 dx + 2/x-2 dx which = x + 2 ln [x-2] + C

And its the same for x/2-x except it would be negative because

x/2-x = -x/x-2

(edited 10 years ago)

Reply 3639

Fortitude

Original post by Revisionbug

Yep, my C4 revision did a complete U-turn after Thurs, & yeah I'm hardly doing any past papers now but instead just like you I'm doing topic based revision so I'm completing questions from the book & looking through past papers at the same time as with C4 the questions tend to be topic based anyway in the exam but obvs the prob now is timing hence I'm really cutting corners so only practising things which look tricky which unfortunately there are a lot of esp in integration & the differential topics. Anyway I just hope that after the C3 shock we've all become immune to the fact that we could get 1 monster of a C4 paper after all, C4 is hard enough as it is. Just don't panic in the exam whatever you do, seriously & now I need to follow my own advice :colondollar: