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Edexcel C3,C4 June 2013 Thread

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Original post by otrivine
Can you not use the substitution method? I think it would be easy to assume that , let 1+sinx be u


This won't work because the derivative of sin x isn't present.
Use cos 2x to replace sin^2 x.
Original post by otrivine
Can you not use the substitution method? I think it would be easy to assume that , let 1+sinx be u


This is what you do, I think! Let me know if I got it right, ha. Sorry about the poor quality, did it on some post it note. Also forgot the "+C" at the end!
photo (22).JPG277.3KB
Original post by nukethemaly
This is what you do, I think! Let me know if I got it right, ha. Sorry about the poor quality, did it on some post it note. Also forgot the "+C" at the end!


makes perfect sense! Its excellent quality , thank you :biggrin:
Original post by otrivine
makes perfect sense! Its excellent quality , thank you :biggrin:


I accidently wrote an extra "+1/2x" there, after I integrated, it was a copying down error! but the final answer is correct, sorry about that
Original post by nukethemaly
I accidently wrote an extra "+1/2x" there, after I integrated, it was a copying down error! but the final answer is correct, sorry about that


No worries! But how come sub method will not work?
Original post by otrivine
No worries! But how come sub method will not work?


Because the derivative of sinx is not to avail.
Vectors are gonna make me miss my A* in maths :frown:
Original post by Bulbasaur
Vectors are gonna
make me miss my A* in maths



Watch some videos on examsolutions.
Hello,
How do Elmwood Papers compare to the real papers that we get in the exam and also how do they compare to the Solomon papers ?
Thank you very much!
Reply 429
Avatar for nm786
nm786
2
Can someone help me with this question please:

the question is to integrate
so far i did:


So,

I expand out the brackets and then get a really horrible quadratic! is there an easier way of doing this?
(edited 11 years ago)
Original post by nm786
Can someone help me with this question please:

the question is to integrate
so far i did:


So,

I expand out the brackets and then get a really horrible quadratic! is there an easier way of doing this?


Instead of trying to put cos²2x in terms of cosx (as you've done on the 2nd line), it's easier to put it in terms of cos4x, using cos4x = 2cos²2x -1. You should know how to do this, if not it's in the textbook (6B or C I think). Just a basic rearrangement though. From there you should end up with something in terms of cos4x and cos2x (i.e. no squares), so it shold be be easy to integrate.
Reply 431
Avatar for nm786
nm786
2
Original post by Bulbasaur
Instead of trying to put cos²2x in terms of cosx (as you've done on the 2nd line), it's easier to put it in terms of cos4x, using cos4x = 2cos²2x -1. You should know how to do this, if not it's in the textbook (6B or C I think). Just a basic rearrangement though. From there you should end up with something in terms of cos4x and cos2x (i.e. no squares), so it shold be be easy to integrate.

so i get cos4x+1=2cos22xcos4x+1=2cos^22x
1/2(cos4x+1)=cos22x1/2(cos4x+1)=cos^22x
subbing this in: 1/2(cos4x+1)−2cos2x+11/2(cos4x+1)-2cos2x+1
∫1/2(cos4x+1)−2cos2x+1\int 1/2(cos4x+1)-2cos2x+1
=(1/4)(1/2)sin4x+x/2−(1/2)2sin2x+x+C=(1/4)(1/2)sin4x+x/2-(1/2)2sin2x+x+C
=1/8sin4x+3/2x−sin2x+C=1/8sin4x+3/2x-sin2x+C. Which is the right answer!
I was working on this one for ages :frown: Cheers mate. :smile:
Original post by nm786
so i get cos4x+1=2cos22xcos4x+1=2cos^22x
1/2(cos4x+1)=cos22x1/2(cos4x+1)=cos^22x
subbing this in: 1/2(cos4x+1)−2cos2x+11/2(cos4x+1)-2cos2x+1
∫1/2(cos4x+1)−2cos2x+1\int 1/2(cos4x+1)-2cos2x+1
=(1/4)(1/2)sin4x+x/2−(1/2)2sin2x+x+C=(1/4)(1/2)sin4x+x/2-(1/2)2sin2x+x+C
=1/8sin4x+3/2x−sin2x+C=1/8sin4x+3/2x-sin2x+C. Which is the right answer!
I was working on this one for ages :frown: Cheers mate. :smile:


Great XD Well done :smile:
Reply 433
Avatar for Better
Better
OP
8
Original post by Bulbasaur
Vectors are gonna make me miss my A* in maths :frown:


No brah you can do it! I had the same problem but I went through all the end of chapter questions.

Key Steps I found
1. Vectors Questions are like a Puzzle - Draw Clear Diagrams and Update yourself with everything you know as you go along
2. Again Draw Clear Diagrams
3. Also don't forget that the vector equation of a line has bigger implications. I.e if an Unknown vector D lies on the Vector Equation it Satisfies the line. So you can equate it to the line equation.

Final note on Vectors don't assume its just basic Algebra, sometimes you will have Circles, and basic triangles, so without a clear diagram its impossible to do any questions. You will just have to use basic logic for the most part on questions where they give you an awkward shape or something different.

Hope that will help a bit - we're all gonna make it brah
(edited 11 years ago)
Original post by Better
No brah you can do it! I had the same problem but I went through all the end of chapter questions.

Key Steps I found
1. Vectors Questions are like a Puzzle - Draw Clear Diagrams and Update yourself with everything you know as you go along
2. Again Draw Clear Diagrams
3. Also don't forget that the vector equation of a line has bigger implications. I.e if an Unknown vector D lies on the Vector Equation it Satisfies the line. So you can equate it to the line equation.

Final note on Vectors don't assume its just basic Algebra, sometimes you will have Circles, and basic triangles, so without a clear diagram its impossible to do any questions. You will just have to use basic logic for the most part on questions where they give you an awkward shape or something different.

Hope that will help a bit - we're all gonna make it brah


Thanks for the help! I have noticed actually that when I draw a bigger and fully detailed diagram i'm much less likely to make mistakes. Usually the last part of a question is quite tricky - but i'll take your advice for that :smile:
Has anyone started any C3/C4 papers yet? If so, what kind of questions you finding difficult?
Original post by Bulbasaur
Vectors are gonna make me miss my A* in maths :frown:


i thought the same, but practice makes perfect. I now can do it all except the last parts where it requires drawing


Original post by The Guide.
Has anyone started any C3/C4 papers yet? If so, what kind of questions you finding difficult?


im thinking its abit too early
mistake i made last year when i did them all and then had nothing :/
do elmwood for now or go over all textbook questions again/review ex or harder textbook questions
Reply 437
Avatar for QwertyG
QwertyG
9
Has anyone started solomon papers??
Original post by The Guide.
Has anyone started any C3/C4 papers yet? If so, what kind of questions you finding difficult?


Yeah, I started them a couple of weeks ago (c4 papers), although i've only done about two papers. Vectors are the most difficult topic for me.
Does anyone recommend Elmwood papers?

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