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Edexcel C3,C4 June 2013 Thread

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Reply 4560
Avatar for KD35
KD35
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Original post by justinawe
The imaginary error function is covered in C4? That's news to me...


You haven't covered the imaginary error function?!

Just kidding, yeah, we can't do it because the power of x isn't linear.
How do you work out percentage error ???????
Original post by silentriver
from the earlier part of the question, we find that when x=2.5 , t=0.5 and t=2. In part c we have to integrate in terms of t, not x. therefore once you intergrate using (y.dx/dt) you can simply put in the t values as the limits and get your answer! I had a confusion in this question too! But instead of using the x values, we can use the t values,either way, you will get the the region enclosed with curve.. hope this helps.


Thank you:smile: but why use the two t values for x=2.5 instead of using the t values for x=2 and x=2.5?
Original post by Mathletic
How do you work out percentage error ???????


Difference between 2 values/Original value.
Original post by Mathletic
How do you work out percentage error ???????



(Unaccurate answer - real answer) / real answer then * 100 = % error
Is 2-4ln2 equivalent to 4ln2-2 :confused:
I can't see any mistakes in my workings and the mark scheme says the second one, but I got the first?!
Thanks.
Original post by Kreayshawn

why can't the cartesian equation be x = ln(root[y+2])
for part b?
correct answer is
y = e^2x - 2


It can be that, it's the same thing. May have not directly said it in the mark scheme, but they'll accept all correct cartesian equations unless they ask for a specific form e.g. y=f(x)
Reply 4567
Avatar for Story
Story
Original post by Zaphod77
With regards to substitution, use the steps I said earlier. Never forget to change the limits, and if one substitution isn't working for you and they didn't specify the substitution you should use, try another - they'll all work out the same in the end. Only use substitution when you have a function of a function! Your second question, the power 3/2 means you square root a number and then cube it. If you had 4^3/2 you would square root it (2) and then cube it (8). If you had x^3/2 you could write it as root(x) * root(x) * root(x), which would then be the same as xroot(x) if you like :smile: With regards to your 3rd question, it doesn't matter at all. They only did it like that in the mark scheme because it involves less steps, but it doesn't matter so long as you get to the right answer :smile: Sorry about the long block of text, my enter key doesn't work on here :frown:


Its fine! Thank you.

You mean like x^2+5/3x... or something along those lines.

Also for integration just say you had 1/cos^2x, although you could change it to sec^2x and get tanx, how come if I try another method my answer is way off? Is there any tips/methods you use to avoid basic mistake e.g illegal cancelling and that sort of stuff?
Original post by Mathletic
How do you work out percentage error ???????




Difference between values, divided by original value.

So if x=2.253 and you got x=2.14, you would find the difference between them which turns out to be 0.113 (2.253-2.14).

Then you use the difference between the actual and estimated value to find the percentage, by dividing it into the actual value.

So 0.113 (the error amount) is divided by the actual amount (2.253). So 0.113 difference is actually about a 5% difference. Remember if you get a value like 0.05 to multiply by 100 to get the percentage! An easy way to know if you are right is if the value seems sensible. It's hardly a 50% error, etc!
Original post by Westeros
Is 2-4ln2 equivalent to 4ln2-2 :confused:
I can't see any mistakes in my workings and the mark scheme says the second one, but I got the first?!
Thanks.


not the same just tap into calculator

Look for minus sign errors is calculation



Edit: Muhahaha First
(edited 10 years ago)
Original post by Westeros
Is 2-4ln2 equivalent to 4ln2-2 :confused:
I can't see any mistakes in my workings and the mark scheme says the second one, but I got the first?!
Thanks.


Just type it into your calculator... :tongue:

You must've made a sign error somewhere.

Edit: beaten to it!

Posted from TSR Mobile
Original post by Chris-69
It can be that, it's the same thing. May have not directly said it in the mark scheme, but they'll accept all correct cartesian equations unless they ask for a specific form e.g. y=f(x)


thanks!

- why are people asking about percentage error, is there a question where they've asked this in the past?
Original post by Westeros
Is 2-4ln2 equivalent to 4ln2-2 :confused:
I can't see any mistakes in my workings and the mark scheme says the second one, but I got the first?!
Thanks.


No, 2-4ln2 = -(4ln2-2)

You must have made some error with positives and negatives somewhere.
What's the hardest paper to do as solomons for c4 seem quite easy?
Original post by President M.E.
What's the hardest paper to do as solomons for c4 seem quite easy?


You could try AEA.
Original post by Story
Its fine! Thank you.

You mean like x^2+5/3x... or something along those lines.

Also for integration just say you had 1/cos^2x, although you could change it to sec^2x and get tanx, how come if I try another method my answer is way off? Is there any tips/methods you use to avoid basic mistake e.g illegal cancelling and that sort of stuff?


A function of a function is like sin(x^2). I was slightly wrong, just realised, as you can use substitutions in other situations, e.g. sinxcosx! The easiest way for that question is to use sec^2x as obviously you don't have to manipulate. What method did you try? To avoid mistakes try more than one way and see if you get the same, or if plug in a value to see if you get the same answer when you have 1/cos^2x and when you have whatever you managed to get (although if you used a substitution that would be a bit harder). Always try to spot the simple solutions, if you can solve it without manipulating then just solve it without making things more complicated :smile:
Good luck to all those sitting the exam tomorrow.
Go in with a positive approach and remember the hard work you have put in to get this far. :smile:
You can't determine the paper you get, you can determine the frame of mind you walk into the exam with.
Original post by Kreayshawn
thanks!

- why are people asking about percentage error, is there a question where they've asked this in the past?


Haha, no idea, not sure why it'd be in our paper.
Original post by justinawe
No, 2-4ln2 = -(4ln2-2)

You must have made some error with positives and negatives somewhere.


Okay nevermind :colondollar: bottom of my fraction should be -2, then 4/-2 gives the -2 and the ln becomes positive?

ImageUploadedByStudent Room1371488630.808643.jpg


Posted from TSR Mobile
(edited 10 years ago)
Original post by President M.E.
What's the hardest paper to do as solomons for c4 seem quite easy?


You better start revising Mechanics then :colondollar:

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