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Killer C4 integral

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The other way is more doing it all in one go in my opinion, it's the same method just done quicker. If you spot good substitutions in any question, use them straight away before attempting integration by parts - that's if the question needs it (generally you end up using just the one method).

Hmm... But shouldn't it work either way? :frown:

Posted from TSR Mobile

Reply 21

CTArsenal

Original post by Branny101

Hmm... But shouldn't it work either way? :frown:

Posted from TSR Mobile

It should, post your working out and I'll check for any errors - a little one could've easily messed it all up :tongue:

Reply 22

Jake011268

I used IBP and u=e^(x^2) so du/dx= 2xe^(x^2) rest was simple and long assess xD

Reply 23

Branny101

Original post by CTArsenal

It should, post your working out and I'll check for any errors - a little one could've easily messed it all up :tongue:

Wait I think I see it :eek:

; if you were going to integrate (xe^(x^2)) how would you do it :rolleyes:

( without substitution)

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Reply 24

miketree

Original post by Branny101

If you were going to integrate (xe^(x^2)) how would you do it? (without substitution)

You cannot integrate this by parts (*), using the substitution

u = x^{2}

is the way to go.

(*) Since

\displaystyle \int e^{x^{2}} \ \mathrm{d}x

cannot be expressed using elementary functions.

(edited 10 years ago)

Reply 25

CTArsenal

Original post by Branny101

Wait I think I see it :eek:

; if you were going to integrate (xe^(x^2)) how would you do it :rolleyes:

( without substitution)

Posted from TSR Mobile

That's pretty difficult to do, I would just stick to substitution when you get to that part because otherwise you put yourself in a pretty awful situation haha.

Reply 26

TenOfThem

Original post by CTArsenal

That's pretty difficult to do, I would just stick to substitution when you get to that part because otherwise you put yourself in a pretty awful situation haha.

No, that bit is easy as it is simply by recognition

Reply 27

interstitial

Original post by Branny101

Wait I think I see it :eek:

; if you were going to integrate (xe^(x^2)) how would you do it :rolleyes:

( without substitution)

Posted from TSR Mobile

That's easy, it's just a simple inverse chain rule integral :s-smilie:

\displaystyle\int xe^{x^{2}} = \dfrac{e^{x^{2}}}{2} + C

Posted from TSR Mobile

(edited 10 years ago)

Reply 28

CTArsenal

Original post by TenOfThem

No, that bit is easy as it is simply by recognition

yup of course, just making the point that you can't do it using IBP.

Substitution still works just takes a little more time (and is pretty much unnecessary I guess) if you can spot that it's just a simple inverse chain rule integral.