# C3 intergration by substitution, help me please!Watch

#1
How do i intergrate dx given that u =
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#2
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#3
So no ones got the balls to answer this question. Im going to bed now hopefully you guys or i will figure it out by tomorrow.
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9 years ago
#4
int 2/u dx

u = e^2x + 4, 0.5 ln (u-4) = x
du/dx = 2e^2x

therefore dx = du/2e^2x

Find the integral of 2 * 2e^2(0.5 ln (u-4)) / u
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9 years ago
#5
(Original post by nevagonafail)
So no ones got the balls to answer this question.
'No ones got the balls' haha. It was just that nobody could be arsed
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9 years ago
#6
(Original post by nevagonafail)
So no ones got the balls to answer this question. Im going to bed now hopefully you guys or i will figure it out by tomorrow.
I'm sorry, remind me to reply instantly next time so as not to anger your superior manhood. We "geniuses of TSR" are of course a disposable resource that don't require any 'pleases' or 'thank yous', and deserve being insulted when we're not instant to suffice your demands; I mean, what are manners on the internet anyway?
9 years ago
#7
(Original post by nuodai)
I'm sorry, remind me to reply instantly next time so as not to anger your superior manhood. I am of course a disposable resource that doesn't require any 'pleases' or 'thank yous', and deserve being insulted when I'm not instant to suffice your demands; I mean, what are manners on the internet?

Rude...
This.

Although I will say that what you've posted doesn't seem to be a very nice integral and I would have thought would be beyond the realms of C3. Where did you get it from?
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9 years ago
#8
(Original post by nevagonafail)
So no ones got the balls to answer this question. Im going to bed now hopefully you guys or i will figure it out by tomorrow.
kthxbai
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#9
(Original post by greenjm90)
This.

Although I will say that what you've posted doesn't seem to be a very nice integral and I would have thought would be beyond the realms of C3. Where did you get it from?

First of all, apologies fore my behaviour it just that i was annoyed with that question. So please can someone help me out. thanks in advance.

Anyway in response to your question, its from the heinnemann AQA book.
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#10
(Original post by GHOSH-5)
kthxbai
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lol that was genuinely funny.
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9 years ago
#11
(Original post by nevagonafail)
How do i intergrate dx given that u =
(Original post by nevagonafail)
How do i intergrate dx given that u =
youre given...

and...

rearrange that to get..

then differentiate it, so...

separate the variables and substitute in x.

so....

subbing in u = f(x)...

hope thats right
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9 years ago
#12
(Original post by Lou Reed)
youre given...

and...

rearrange that to get..

then differentiate it, so...

[/latex]

hope thats right
Up to there I see what you've done is right, but I've never seen anyone seperate the variable for this?

You only need to seperate the variables when you have to integrate a function with both x and y's.
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9 years ago
#13
(Original post by giran)
Up to there I see what you've done is right, but I've never seen anyone seperate the variable for this?

You only need to seperate the variables when you have to integrate a function with both x and y's.
no im pretty sure you need to separate the variables here to get (int)dx in terms of (int)du.

anyways i got the right answer =]
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9 years ago
#14
(Original post by Lou Reed)
no im pretty sure you need to separate the variables here to get (int)dx in terms of (int)du.

anyways i got the right answer =]
That's stange, normally you'd make it in terms of U hence substitution. integrate with respect to U then stick u = whatever.

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9 years ago
#15
(Original post by giran)
That's stange, normally you'd make it in terms of U hence substitution. integrate with respect to U then stick u = whatever.

i thnk were arguing the same point here..

we need to turn

into terms of u, ye?

so i need to convert the into terms of so i can integrate with respect to u.

so...

btw, is my final integration wrong?
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#16
(Original post by Lou Reed)
i thnk were arguing the same point here..

we need to turn

into terms of u, ye?

so i need to convert the into terms of so i can integrate with respect to u.

so...

btw, is my final integration wrong?

0
9 years ago
#17
(Original post by Lou Reed)
i thnk were arguing the same point here..

we need to turn

into terms of u, ye?

so i need to convert the into terms of so i can integrate with respect to u.

so...

btw, is my final integration wrong?
you're confusing two different methods here.
The answer OP posted was the same one I got. Op that is correct.

Then you plug it back into your original question but in terms of u.
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9 years ago
#18
(Original post by nevagonafail)
lol that was genuinely funny.
Did you eventually find the solution, somewhere within the maze of the 59 spoilers?
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#19
(Original post by GHOSH-5)
Did you eventually find the solution, somewhere within the maze of the 59 spoilers?
Yes, i did thats why i found it funny. Though I'd rather you give me the answer straight next time.
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9 years ago
#20
(Original post by giran)
(Original post by nevagonafail)
yeah thats what i got...(from my previous post)...

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