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# Edexcel C3 (20/06) Revision Thread watch

1. (Original post by Slice'N'Dice)
Yeah, what does these bits refer to though?
x0 is simply the number 2.4, which they give you.

To get x1 you put 2.4 into the formula

To get x2 you put x1 into the formula

To get x3 you put x2 into the formula

So....

x1 = 4 - ln2(2.4) = 4 - ln4.8 = 2.431384082

x2 = 4 - ln2(2.431384082) = 2.418392143

x3 = 4 - ln2(2.418392143) = 2.423749904

Tip - Type x0 into your calculator, press "=", then use the "Ans" button to type a general formula. Then just keep pressing "="

e.g. 4 - ln2Ans
2. (Original post by seankhn)
x0 is simply the number 2.4, which they give you.

To get x1 you put 2.4 into the formula

To get x2 you put x1 into the formula

To get x3 you put x2 into the formula

So....

x1 = 4 - ln2(2.4) = 4 - ln4.8 = 2.431384082

x2 = 4 - ln2(2.431384082) = 2.418392143

x3 = 4 - ln2(2.418392143) = 2.423749904

Tip - Type x0 into your calculator, press "=", then use the "Ans" button to type a general formula. Then just keep pressing "="

e.g. 4 - ln2Ans
Oh! I get it now!

Many thanks seankhn.
3. Given that p=secθ-tanθ and q=secθ+tanθ show that p=1/q

Pretty sure I did this before but can't do it now
4. (Original post by SunGod87)
Given that p=secθ-tanθ and q=secθ+tanθ show that p=1/q

Pretty sure I did this before but can't do it now
pq = (secx - tanx)(secx + tanx)

= sec²x - tanxsecx + tanxsecx - tan²x

= sec²x - tan²x

= 1

pq = 1

p = 1/q

I used x instead of theta. Meh
5. (Original post by seankhn)
I doubt they'll go out of their way to cover something which is completely irrelevant to C3 like sequences and series. I have a suspicion it'll be something like using the laws of logarithms and then having to draw a graph.
Me too
6. seankhn: Thanks, it was the one I had done before, forgot how to do it lol
7. (Original post by SunGod87)
seankhn: Thanks, it was the one I had done before, forgot how to do it lol
I've got solutions for all those mixed exercise questions
8. What are even/odd functions? =o
9. Even functions:
f(x) = f(-x)
The function is a reflection of itself in the y-axis. Example: cosx

Odd functions:
f(x) = -f(x)
The function is a 180 degree rotation of itself. Example: sinx
10. Thanks man! For the 180 degree rotation, what does it mean by example:sinx?
11. Imagine drawing the postive side of sinx, and then rotating it 180° (about the origin). You'd get the negative part of it. So, f(x) = sinx is an odd function.
See attachment...
Attached Images

12. Ah skeen. Cheers =o)
13. (Original post by seankhn)
No problem.

Anyone had a go at that sin3x = cosx question yet? The interval is 0 to 360°

sin3x = cosx
sin(x+2x) = cosx
sinxcos2x+cosxsin2x = cosx
sin(1-2sin²x)+2cos²sinx = cosx
sinx(1-2sin²x+2cos²x) = cosx
sinx(1-2(sin²x+cos²x)) = cosx
-sinx = cos x
tanx = -1
x = 135, 315
14. (Original post by Seth)
sin3x = cosx
sin(x+2x) = cosx
sinxcos2x+cosxsin2x = cosx
sin(1-2sin²x)+2cos²sinx = cosx
sinx(1-2sin²x+2cos²x) = cosx
sinx(1-2(sin²x+cos²x)) = cosx
-sinx = cos x
tanx = -1
x = 135, 315
After this stage.....

sinx(1-2sin²x+2cos²x) = cosx

Would factorising further not give you....

sinx(1-2(sin²x-cos²x)) = cosx???

If so, how do I then go about completing the question?

Cheers.
15. there should not be a minus in your factorisation

sin²x + cos²x = 1
16. (Original post by mik1w)
there should not be a minus in your factorisation

sin²x + cos²x = 1
But it's -2sin²x + 2cos²x

sin²x + cos²x isn't a factor of that.
17. why does sec^2x-tan^2x =1?

EDIT: its cos tan^2x +1 = sec^2x
18. By the way, edexcel practice papers made by edexcel themselves are the best papers you can do. I've done the c2 ones and one of them is very much like the jan 05 paper. I'd recommend them over solomon papers.
19. Indeed. Btw, is it just me or does paper A3's first q not show up?
20. It doesnt show up.
I need help with this.

f(x) = 1/(x+1)(x-1)

What is the range? The answers just say the range of f(x) is y where y>0

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