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# Edexcel C3,C4 June 2013 Thread Watch

1. Anyone on here doing s3?

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2. (Original post by Zaphod77)
I'll be honest, I've always used the quadrant way You must make sure you know the shapes of the graphs, but it doesn't matter which method you use so long as you get the right answer And yeah, basically, you just have to consider the shape of the graph and where it's the same, as it's still recurring
Ok, thank you!

Also, I have a some questions, I hope its not too much trouble to ask you.

There was a question on c3 with differentiating something like ln3t, the problem was I dont know when to tell if its ln(3t) or ln(3)t and this question had no brackets on either so what do you assume??

Just say you have to solve sin(2x+20)=0 and the limits are 0 to 360, do you times by 2 so the limits you get are 0 720 then add 20 so the final limits are 20 to 740, does the same apply for (2x-20), instead you just take away from the original limits so its -20 to 700 ?
3. (Original post by justinawe)
If P is a turning point on the curve y=f(x), and the x-coordinate of P is , then:

Yeah I knew that I just couldn't work out how they rearranged it to give that answer, thank you anyway

(Original post by Scorcher)
Let me know if you don't understand the method and I will try to explain further.

Attachment 225937
Thankyouuu! I got confused at first, then I realised you use x instead of curly x's
4. (Original post by Story)
Ok, thank you!

Also, I have a some questions, I hope its not too much trouble to ask you.

There was a question on c3 with differentiating something like ln3t, the problem was I dont know when to tell if its ln(3t) or ln(3)t and this question had no brackets on either so what do you assume??

Just say you have to solve sin(2x+20)=0 and the limits are 0 to 360, do you times by 2 so the limits you get are 0 720 then add 20 so the final limits are 20 to 740, does the same apply for (2x-20), instead you just take away from the original limits so its -20 to 700 ?
First question: They should put in the brackets or italicise the bits going in the ln! If they don't I would take it as ln(3) x t, but it's a difficult call, they should put it in brackets if it's ambiguous. Second question: Yes, exactly that
5. (Original post by Zaphod77)
First question: They should put in the brackets or italicise the bits going in the ln! If they don't I would take it as ln(3) x t, but it's a difficult call, they should put it in brackets if it's ambiguous. Second question: Yes, exactly that
Thank you!!

Also a general thing about trig identities...e.g we know tanx=sinx/cosx, but if you square both sides the tan^2x=sin^2x/cos^2x. Can we do this to any trig identitiy to manipulate it and get what we want. Is there anything that could be done when manipulating to avoid mistakes?
I know this is basic stuff i just want to be positive.

Do you have any tips for domain range questions they always seem to catch me out?
and also the modulus of f(modulus of x only) is a reflection in the y axis, where the x value is positive before we put it in?

C3 jan 13 q)5i) was where I was unsure as there are no brackets on either the 2 or 2x as a whole to clarify?
6. When you have to make the iteration formula yourself, do you just make x the subject?
7. (Original post by Story)
Thank you!!

Also a general thing about trig identities...e.g we know tanx=sinx/cosx, but if you square both sides the tan^2x=sin^2x/cos^2x. Can we do this to any trig identitiy to manipulate it and get what we want. Is there anything that could be done when manipulating to avoid mistakes?
I know this is basic stuff i just want to be positive.

Do you have any tips for domain range questions they always seem to catch me out?
and also the modulus of f(modulus of x only) is a reflection in the y axis, where the x value is positive before we put it in?
I would recommend not squaring where possible because the opposite, square rooting, has 2 answers (positive and negative). Always use the trig identities where possible, if they're asking for something in a show that then manipulate it as much as you like until you get there, but in general there'll be simple ways to get where you want using trig identities. We always got told to write down every trig identity in a table on those questions so then we had something to look at when choosing which one to use, as it's easier to see the one you need! Domain and range catch everyone out, they're not easy. What I would recommend is draw the graph out if you can, it helps you see which way an inequality should go! Yeah, the 2 sides of the y-axis are a reflection of each other
(Original post by Anonymous1717)
When you have to make the iteration formula yourself, do you just make x the subject?
Yes, but get it in terms of x - don't get it completely on its own!
8. Just had an exam this afternoon And I've got only about 5 hours to prepare for C3 really... anyone got any tips? Will probably get through 3 past papers at most, so does anyone have any recommendation on which 2-3 I should do? (solomon/edexcel)

Thanks

(Original post by Anonymous1717)
When you have to make the iteration formula yourself, do you just make x the subject?
yup
9. (Original post by Zaphod77)
I would recommend not squaring where possible because the opposite, square rooting, has 2 answers (positive and negative). Always use the trig identities where possible, if they're asking for something in a show that then manipulate it as much as you like until you get there, but in general there'll be simple ways to get where you want using trig identities. We always got told to write down every trig identity in a table on those questions so then we had something to look at when choosing which one to use, as it's easier to see the one you need! Domain and range catch everyone out, they're not easy. What I would recommend is draw the graph out if you can, it helps you see which way an inequality should go! Yeah, the 2 sides of the y-axis are a reflection of each other

Yes, but get it in terms of x - don't get it completely on its own!
Ok, Great! So just to clarify try and stick to original trig identities when you can?

Thank you so much by the way!
10. (Original post by Story)
Ok, Great! So just to clarify try and stick to original trig identities when you can?

Thank you so much by the way!
Yeah, basically. Good luck! No problem
11. (Original post by Zaphod77)
Yeah, basically. Good luck! No problem
Good Luck!
12. (Original post by JenniS)
how do you do that question?
You use the formula cosx = sin(90-x)
13. (Original post by JenniS)
how do you do that question?
sorry for the late reply.
y=arccosx
cosy=x
now draw a right triangle with with angle y on the left, adjacent is x and hypotenuse is 1.
now we want arcsinx in terms of y. call arcsinx a letter - m so sinm = x
now back to the triangle label m. Now you know that angles in a triangle add up to 180 (pi) so let m+y+pi/2=pi so m=-y+pi/2. Therefore arcsinx=-y+pi/2
14. (Original post by Story)
Ok, Great! So just to clarify try and stick to original trig identities when you can?

Thank you so much by the way!
What are the "original" ones?
15. what would people say are the trickiest questions?

dont know what to do for last minute prep!
16. Do we have to know about half angles in trig, if so, what are they?
And could the arcsin, arctan, arccos graphs come up?
17. Never really seen the use of factor formula could come up!! Would do guys think???

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18. (Original post by Westeros)
When I was working this out, I also got 2.0988... etc, the mark scheme actually says 'Either awrt 2.1 or awrt 6.7', so that's still the correct answer when you round!

To get the final answers, this part is quite easy when you find out what you have to do! so now you have 2 times, 2.0988 and 6.711... etc, each of these mean 2 hours and ____ minutes, or for the other value, 6 hours and ____ minutes, however we need to convert them into minutes since they are currently in hours.

So for t=2.0988
We take the 0.0988 and multiply it by 60 which gives 5.928 minutes
Add that onto the 2 hours (on a 24 hour clock), we get 14:06

And for t=6.71136...
Take the 0.71136, multiply it by 60 to get the minutes = 42.68.. mins
Add that onto the 6 hours, and we get 18:43 when rounded

Hope this helped
Thank you sososo much! You really explained it well!
Just wondering, you know in some trig questions when you have for example sin(2x+35.2) = 0.5 and you need to find x, is it okay to let a letter e.g. b=2x+35.2? Then continue working it out (sinb=0.5, b=30) etc etc. I get the right answers its just that the mark schemes normally don't do this but I find it easier
Good luck for tomorrow btw
19. (Original post by Crazy Crouton)
Do we have to know about half angles in trig, if so, what are they?
And could the arcsin, arctan, arccos graphs come up?
https://www.google.co.uk/search?q=ha...05uWSIm7aDM%3A

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20. (Original post by ytop2)
does anyone know how i would integrate (e^x^2)^2 ?
2 ways of doing the chain rule

differentiate from start
(e^x^2)^2
(2)(2x)(e^x^2)(e^x^2)^2-1
4x(e^x^2)(e^x^2)
4xe^2x^2

the other way is easier, first expand
(e^x^2)^2
(e^x^2)(e^x^2)
e^2x^2
then differentiate
(4x)(e^2x^2)
4xe^2x^2

can someone post really hard question to do with exponential decay and one to do with trig.

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