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Is my integral correct?

Hi so just wanted to clarify that this...

[br]cos(x)+x2+1x[br][br]\int cos(x) +\dfrac{x^2 +1}{x}[br]

Can integrate to...

[br]sin(x)+(x2+1)lnx+c[br][br]sin(x) + (x^2 +1) \ln |x| + c[br]

Thanks in advance, the mark scheme has something different but just like the thread earlier today I want to clarify I'm doing this right :smile:
Original post by 01Chris02
Hi so just wanted to clarify that this...

[br]cos(x)+x2+1x[br][br]\int cos(x) +\dfrac{x^2 +1}{x}[br]

Can integrate to...

[br]sin(x)+(x2+1)lnx+c[br][br]sin(x) + (x^2 +1) \ln |x| + c[br]

Thanks in advance, the mark scheme has something different but just like the thread earlier today I want to clarify I'm doing this right :smile:


This isn't correct, I'd separate your fraction into two separate ones and then you should be able to see your mistake :smile:


Posted from TSR Mobile
Original post by 01Chris02
Hi so just wanted to clarify that this...

[br]cos(x)+x2+1x[br][br]\int cos(x) +\dfrac{x^2 +1}{x}[br]

Can integrate to...

[br]sin(x)+(x2+1)lnx+c[br][br]sin(x) + (x^2 +1) \ln |x| + c[br]

Thanks in advance, the mark scheme has something different but just like the thread earlier today I want to clarify I'm doing this right :smile:


Close! Obviously the cosx is correct but you should split the fraction and try from there :smile:

EDIT: Just seen the post above me, oops, was too late! :tongue:
Reply 3
So is a general rule to fully factorize and split? Then integrate? I was differentiating then denominator and then multiplying it by a term (n) so that it gave the numerator. Then putting it in the form...

[br]nlndenom[br][br]n \ln |denom| [br]

This was what my teacher had said to do! :/

Thanks guys so far! :smile:

EDIT: Does this only apply to making n a constant and not a variable?
(edited 10 years ago)
Original post by 01Chris02
So is a general rule to fully factorize and split? Then integrate? I was differentiating then denominator and then multiplying it by a term (n) so that it gave the numerator. Then putting it in the form...

[br]nlndenom[br][br]n \ln |denom| [br]

This was what my teacher had said to do! :/

Thanks guys so far! :smile:

EDIT: Does this only apply to making n a constant and not a variable?


Well whenever I integrate I always make sure everything is in its simplest form first and to split up fractions, unless you can see that the numerator is the derivative of the denominator, in which case you should know what it integrates to :smile:


Posted from TSR Mobile
Reply 5
Original post by MathsNerd1
Well whenever I integrate I always make sure everything is in its simplest form first and to split up fractions, unless you can see that the numerator is the derivative of the denominator, in which case you should know what it integrates to :smile:


Posted from TSR Mobile

That's great thanks, I actually feel ready for C3 tomorrow! :biggrin: All past papers done now and this was the last issue I had! Thanks!
Original post by 01Chris02
That's great thanks, I actually feel ready for C3 tomorrow! :biggrin: All past papers done now and this was the last issue I had! Thanks!


Glad I could help and best of luck with your exam! If you need any more help I'll be happy to help :smile:


Posted from TSR Mobile
Reply 7
Original post by 01Chris02
Hi so just wanted to clarify that this...

[br]cos(x)+x2+1x[br][br]\int cos(x) +\dfrac{x^2 +1}{x}[br]

Can integrate to...

[br]sin(x)+(x2+1)lnx+c[br][br]sin(x) + (x^2 +1) \ln |x| + c[br]

Thanks in advance, the mark scheme has something different but just like the thread earlier today I want to clarify I'm doing this right :smile:


close but no... seperate the fraction :smile: I bet you that the ms has 0.5x^2+ln(x) where you have (x^2+1)ln(x)

bear in mind that in your problem the top and bottom are BOTH functions of x
Reply 8
Original post by 01Chris02
Hi so just wanted to clarify that this...

[br]cos(x)+x2+1x[br][br]\int cos(x) +\dfrac{x^2 +1}{x}[br]

Can integrate to...

[br]sin(x)+(x2+1)lnx+c[br][br]sin(x) + (x^2 +1) \ln |x| + c[br]

Thanks in advance, the mark scheme has something different but just like the thread earlier today I want to clarify I'm doing this right :smile:


The first part is fine but you played an "illegal move" on the second part. The reason is that if you tried differentiating your result, you'd have to use the product rule. Like others have said, try splitting it up which would make it a lot easier :smile:

Good luck in your exam
Reply 9
Thanks guys, you've been a big help! :smile:

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