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Maths integration help needed!

I've forgotten how to integrate functions in the form of a fraction where the integral is not a log natural... can someone help me with this question?

2 / (x-2)^2
(edited 8 years ago)
Reply 1
change it into the form 2(x-2)^-2

then divide by the new power which would be -1, since the coefficient of x is 1 it has no effect

dividing 2 by -1 gives -2

so it becomes -2(x-2)^-1

edit: you can also test the answer by differentiating it, so -1 x -2 = 2

so therefore 2 x (x-2)^-2 = 2(x-2)^-2 which is the original function
(edited 8 years ago)
Reply 2
Original post by AndyOC
I've forgotten how to integrate functions in the form of a fraction where the integral is not a log natural... can someone help me with this question?

2 / (x-2)^2


Rewrite that as 2dx(x2)2=2(x2)2dx\displaystyle 2 \int \frac{\mathrm{d}x}{(x-2)^2} = 2 \int (x-2)^{-2} \, \mathrm{d}x using the fact that 1ab=ab\frac{1}{a^b} = a^{-b}.

Then use the fact that xndx=xn+1n+1+C\displaystyle \int x^n \, \mathrm{d}x = \frac{x^{n+1}}{n+1} + \mathcal{C}, what does that get you?
Reply 3
Oh, and moved to maths.
Reply 4
Original post by C-rated
change it into the form 2(x-2)^-2

then divide by the new power which would be -1, since the coefficient of x is 1 it has no effect

dividing 2 by -1 gives -2

so it becomes -2(x-2)^-1

edit: you can also test the answer by differentiating it, so -1 x -2 = 2

so therefore 2 x (x-2)^-2 = 2(x-2)^-2 which is the original function


Original post by Zacken
Rewrite that as 2dx(x2)2=2(x2)2dx\displaystyle 2 \int \frac{\mathrm{d}x}{(x-2)^2} = 2 \int (x-2)^{-2} \, \mathrm{d}x using the fact that 1ab=ab\frac{1}{a^b} = a^{-b}.

Then use the fact that xndx=xn+1n+1+C\displaystyle \int x^n \, \mathrm{d}x = \frac{x^{n+1}}{n+1} + \mathcal{C}, what does that get you?


got it thank you!:smile:
Reply 5
Original post by Zacken
Rewrite that as 2dx(x2)2=2(x2)2dx\displaystyle 2 \int \frac{\mathrm{d}x}{(x-2)^2} = 2 \int (x-2)^{-2} \, \mathrm{d}x using the fact that 1ab=ab\frac{1}{a^b} = a^{-b}.

Then use the fact that xndx=xn+1n+1+C\displaystyle \int x^n \, \mathrm{d}x = \frac{x^{n+1}}{n+1} + \mathcal{C}, what does that get you?


what about this one? x / (4 - x^2)^1/2 dx
Reply 6
Original post by AndyOC
what about this one? x / (4 - x^2)^1/2 dx


Use the substitution u=4x2u = 4-x^2.
Reply 7
thank you once again:biggrin:
Reply 8
Original post by AndyOC
thank you once again:biggrin:


No problem.
Reply 9
Original post by Zacken
Use the substitution u=4x2u = 4-x^2.


Surely inspection is the easiest method here.
Reply 10
Original post by B_9710
Surely inspection is the easiest method here.


That's the way I'd do it as well, but he didn't spot the inspection so I suggested the sub. Which is fairly equivalent, really.
Reply 11
Original post by Zacken
That's the way I'd do it as well, but he didn't spot the inspection so I suggested the sub. Which is fairly equivalent, really.

In an exam it's best to do both methods to double check, you don't want to be losing marks when it comes to something as trivial as integration
Reply 12
Original post by C-rated
In an exam it's best to do both methods to double check, you don't want to be losing marks when it comes to something as trivial as integration


Agreed.

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