printergirl
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#1
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#1
integrate ln(x+2) by parts
my working: u=lnx+2 du/dx =1/x+2, dv/dx=1 v=1 woops meant x
this makes
xln(x+2)-integral of x/x+2
i got xln(x+2)-x+0.25x2+c

however in the mark scheme it says this
(x+2) \ln(x+2) -x + k
is my answer the same? and if it is would i be awared the full marks
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Enginerd.
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#2
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(Original post by printergirl)
integrate ln(x+2) by parts
my working: u=lnx+2 du/dx =1/x+2, dv/dx=1 v=1
this makes
xln(x+2)-integral of x/x+2
i got xln(x+2)-x+0.25x2+c

however in the mark scheme it says this
(x+2) \ln(x+2) -x + k
is my answer the same? and if it is would i be awared the full marks
"dv/dx=1 v=1"

This is wrong. If DV/DX = 1, v = X.
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printergirl
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(Original post by Enginerd.)
"dv/dx=1 v=1"

This is wrong. If DV/DX = 1, v = X.
thats a typo i used v=x in my workings
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printergirl
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#4
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#4
also can someone help me with this question
5ii, how did they get root 13
http://www.thestudentroom.co.uk/atta...9&d=1340294617
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GeneralOJB
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Did you seriously divide x/x+2 into x/x + x/2? :eek:

Use substitution u=x+2
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TenOfThem
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#6
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#6
(Original post by printergirl)
integrate ln(x+2) by parts
my working: u=lnx+2 du/dx =1/x+2, dv/dx=1 v=1 woops meant x
this makes
xln(x+2)-integral of x/x+2
i got xln(x+2)-x+0.25x2+c

however in the mark scheme it says this
(x+2) \ln(x+2) -x + k
is my answer the same? and if it is would i be awared the full marks
Why would

\int \dfrac{x}{x+2} dx = -x + \dfrac{x^2}{4}
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printergirl
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(Original post by GeneralOJB)
Did you seriously divide x/x+2 into x/x + x/2? :eek:

Use substitution u=x+2
can you not do that?? edit oh i cbest made now than in the exam

can any1 do question 5ii, how did they get root 13
http://www.thestudentroom.co.uk/atta...9&d=1340294617


how do you split x/x+2
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TenOfThem
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#8
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(Original post by GeneralOJB)
Did you seriously divide x/x+2 into x/x + x/2?
Good spot

They had me baffled with that one
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TenOfThem
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#9
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#9
(Original post by printergirl)
can you not do that??
How would you think that you can?
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printergirl
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#10
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(Original post by TenOfThem)
How would you think that you can?
:cry::cry2: how do i split it?
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TenOfThem
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#11
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(Original post by printergirl)
...
No need for the neg
It was a serious question

I was trying to find out what your misconception was
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TenOfThem
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#12
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(Original post by printergirl)
:cry::cry2: how do i split it?
You can't

Well, you can but you need to either use substitution or

(my preference)

\dfrac{x}{x+2} = \dfrac{x+2-2}{x+2} = \dfrac{x+2}{x+2} - \dfrac{2}{x+2} = 1 - \dfrac{2}{x+2}

Giving something that you can integrate

You can split the denominator but not the numerator
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printergirl
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#13
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#13
(Original post by TenOfThem)
No need for the neg
It was a serious question

I was trying to find out what your misconception was
u seemed very rude

how do i split x/x+2 ????
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TenOfThem
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#14
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#14
(Original post by printergirl)
u seemed very rude

how do i split x/x+2 ????
so do you

I have answered your question, there was no need to repeat
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