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Official Edexcel C3 Discussion Thread watch

1. I just got 69/75 in a very easy paper. I made a silly mistake when I was solving trig. equations. I always neglect the ranges they give you!
2. Aaaaah, I'm psyched for this exam!

I need 90% to get halfway to that A*...
3. (Original post by jj.)
I went through the book first, picked up on anything that was my weakness and then I started past papers. It's best to understand C3 first before doing the papers, if you understand it, the papers should be a breeze.
(Original post by .:excel4100%:.)
Yeah, go through the text book and start to understand the topics! Then start practice papers so you can get used to the format of the papers and timing also!

If you do like all the Solomons and then the edexcel past papers, I can almost guarantee you will get at least an A!!
Ok. So textbook then past papers it is...Thanks guys. I have 4 days left...is it possible? I spent Xmas revising for resits...hence, the lack of time.
4. Ok quick question, why is the range of the curve greater or equal to 1, and not just greater than 0?
5. (Original post by samir12)
Ok quick question, why is the range of the curve greater or equal to 1, and not just greater than 0?
Well for the graph of , x would have to negative for the y to be less than one. However since it's it cannot be negative hence the minimum value of y is 1 (when x=0)
6. General C3 question: Will I be forced to use the remainder theorem in the exam for a question? (I find the long division method easier)
7. I've been slamming my head into the wall trying to mark my answers to question papers. For the trig proofs, I always get there in the end but a different way to what's given in the mark scheme. Will I still get full marks for these questions, as long as I don't make any mistakes?
8. (Original post by milliondollarcorpse)
Well for the graph of , x would have to negative for the y to be less than one. However since it's it cannot be negative hence the minimum value of y is 1 (when x=0)
Thanks mate, now I understand.
9. (Original post by gottastudy)
General C3 question: Will I be forced to use the remainder theorem in the exam for a question? (I find the long division method easier)
Yes, it only takes like 10 seconds to learn
10. (Original post by xSkyFire)
Yes, it only takes like 10 seconds to learn

I get the comparing coefficients part, just not really setting up the equation in the form.

Will it always be (divisor)....

11. (Original post by gottastudy)

I get the comparing coefficients part, just not really setting up the equation in the form.

Will it always be (divisor)....

Quotient x divisor + remainder, really straightforward. Just do the mixed exercises in chapter 1, C3 and it'll become clear
12. (Original post by xSkyFire)
Quotient x divisor + remainder, really straightforward. Just do the mixed exercises in chapter 1, C3 and it'll become clear
I already have done! Except I used long division...It didn't say in particular to use the remainder theorem!

I don't get why in example 13, it's Dx + E and in example 12 why it's just + D (remainder part)? Is this to do with the powers?

No worries. I figured it out.
13. (Original post by typewriter)
Will I still get full marks for these questions, as long as I don't make any mistakes?
yes.
14. need help with this

Given that x = 4 sin (2y + 6), find dy/dx in terms of x.

my answer to the Q was dy/dx= 1/8cos(2y+6)
but i didnt know how to write it in term of x can someone help me plz
15. how would you do this

if f(x)= 4-x^2

solve ff(0)
so 4-(4-x^2)^2
x^4-8x^2-12=0

i dont know how i would do it.
xxx
16. (Original post by taherq)
need help with this

Given that x = 4 sin (2y + 6), find dy/dx in terms of x.

my answer to the Q was dy/dx= 1/8cos(2y+6)
but i didnt know how to write it in term of x can someone help me plz
Rearrange x =4sin (2y + 6) in terms of y and substitute it into dy/dx
(Original post by indie_couture)
how would you do this

if f(x)= 4-x^2

solve ff(0)
so 4-(4-x^2)^2
x^4-8x^2-12=0

i dont know how i would do it.
xxx
Let x^2=y

Solve y^2-8y-12=0
17. AAAAAAAh c3! Does anyone have any tips? I can do all the questions I think, it's just carelessness that lets me down. I'm aiming for an A* as well Any advice?
18. can someone tell me why... cos5x-cosx = -2sin3xsin2x
19. (Original post by MIKE ESSIEN IS QUITE SICK)
can someone tell me why... cos5x-cosx = -2sin3xsin2x
check your c3 text book. this is an identity that you have to learn.
=-2sin(5x+x/2)sin(5x-x/2)
=-2sin3xsin2x
20. (Original post by MIKE ESSIEN IS QUITE SICK)
can someone tell me why... cos5x-cosx = -2sin3xsin2x
The trig identity for is in the formula booklet: .

If you meant you wanted the proof:

Use the identities

and

Subtract one from the other

Let and
so, and

Therefore,

And in your case, you'd just sub in the and as and

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