Shoutbox

can someone please solve this integration problem for me? i have been trying it since a week, gone mad trying to solve it. please help.
(ps: its solvable. answer exists.)


edit: "x.x" means x square.

could some one do it?
plz reply.

Well... the square root of x^2 1/x^2 is just x + 1/x isn't it?

So...

quote:

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Originally posted by andrewdodd13
Well... the square root of x^2 1/x^2 is just x + 1/x isn't it?

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No it isn't...

The square root of x * x = x... So the square root of x * x + a, where a > 0, is greater then x... Right?

When x > 0, 1 / (x * x) > 0, so the square root will be greater then x. You see?

The integral of that formula is hard to find... and it's been a while since I have been integrating formulas...

Ok well I'm quite sure you have to use integration by parts. I will update this post when I get the answer for you.

EDIT: I had a go and it was terribly off, probably some little mistake somewhere.  Anyway instead of trying again I used Maple and it only gave me:

2*(x^3+1/x+x/(x^4+1))^(3/2)/(3*x^2-1/x^2+1/(x^4+1)-4*x^4/(x^4+1)^2)

That was after a bit of work of course.  Seemed it missed being able to do a reverse chain rule .  I tried simplifying it but I couldn't find anything, maybe someone else can help.  I hope this helps you. 

quote:

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Originally posted by andrewdodd13
Well... the square root of x^2 1/x^2 is just x + 1/x isn't it?

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wtf?
If that were true most of the maths problems in the world would be solved in a few steps

i dont think this can be done by parts. i tried using it, but the expression we get inside the second integration sign is even more complicated than the question itself.
i tried substituting different forms of the expression, that hasnt helped me yet. i tried adding and substrating different terms like (x^3+1/x^3) to get some sort of differentiable term, but with not much success.
i even tried substituting trigonometric properties, but that doesnt help either.

have you tried changing variables like sen( u) = x ? Or maybe the good old Tan(x/2) ? i dunno it just looks like it could be possible with one of those, im too lazy to try now though maybe tomorrow

quote:

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Originally posted by Chrono
have you tried changing variables like sen( u) = x

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sin wont do it. Bleh it could but i cba to work with (sin(u))^4

quote:

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Originally posted by Chrono
Or maybe the good old Tan(x/2) ?

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Isnt that for places where you have trignometrics in the numerator and denominator?

I was thinking of something like x^2 = (sin(u))^2 or something like that. cba atm. mabbe after my exams

nups, i already tried various trigo properties, none work.