Unsure where the negative sign comes from -- integration Watch

anonymous230
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From the edexcel pure year 2 book, I'm unsure where the negative sign comes from, I understand everything else in the question:

They are working out the area of A1 why's there a negative sign in front of the entire thing on it all, final answer is the same as the one in the book:


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my final answer ends up being :

0.25 * (2e^(-1) - 1)
instead of
0.25 * (1 - 2e^(-1))
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0le
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The second last step is probably where you messed up, but since you don't show your working out, we can't really say for sure.
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anonymous230
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sorry heres my working out hope its clear enough to read, the part above is just defining u=x du/dx = 1 , the same as the one in the solution book, everythings the same but i dont get the negative sign on the 2nd and 3rd last lines of the solution

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0le
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So yes, it is the second last step. You should break it down into more steps. Where you've substituted zero and -1/2 into the already integrated equation, do this step n several parts.

Essentially you are meant to get +1/4 instead of -1/4 because the bit in square brackets, when substituting zero, will give -1/4 and there will still be a negative sign outside the square brackets.
Last edited by 0le; 4 days ago
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anonymous230
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(Original post by 0le)
So yes, it is the second last step. You should break it down into more steps. Where you've substituted zero and -1/2 into the already integrated equation, do this step n several parts.
is it ? i got the exact same thing apart from the giant brackets around it all with a negative sign, which came from the 3rd last step, why is there a negative sign before the square brackets?
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0le
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(Original post by anonymous230)
is it ? i got the exact same thing apart from the giant brackets around it all with a negative sign, which came from the 3rd last step, why is there a negative sign before the square brackets?
I think it is related to the fact the region is underneath the curve:
http://www.mathcentre.ac.uk/resource...eas-2009-1.pdf

But will need someone else to confirm or suggest otherwise.
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anonymous230
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(Original post by 0le)
I think it is related to the fact the region is underneath the curve:
http://www.mathcentre.ac.uk/resource...eas-2009-1.pdf

But will need someone else to confirm or suggest otherwise.
im honestly not sure it could be something ive forgotten thanks a lot for ur help n efforts
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zetamcfc
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(Original post by anonymous230)
im honestly not sure it could be something ive forgotten thanks a lot for ur help n efforts
You are trying to find an area. You can't have a negative area. You have evaluated the definite integral correctly, but that is not what the question is asking.

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Hope this is correct, my recent history on helping with A-level stuff isn't great lol, back to some representations
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anonymous230
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(Original post by zetamcfc)
You are trying to find an area. You can't have a negative area. You have evaluated the definite integral correctly, but that is not what the question is asking.

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Hope this is correct, my recent history on helping with A-level stuff isn't great lol, back to some representations
AHHH thats what it is lol didnt even realise yeh ur right thanks lol
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