Integration Problem - Help!!

danza · 13 Feb 2011 at 16:10

I'm doing some integration by parts, and I cannot for the life of me work out how the first equation becomes the second:

This is taken from class notes which I'm writing up, but it has me stumped. Apparently it's correct, but I just can't see it, namely where the -1/25 x e^5x comes from. :confused:

skippy2421 · 13 Feb 2011 at 16:13

integration by parts my dear friend. Only just woke up so cba to go through it.

Like i said find the formula for integration by parts, let u be x and dv be e^5x.

The second equation is right btw just tried it.

TheCenturion · 13 Feb 2011 at 16:14

images are blocked for me atm. Could you possibly type the equation so that I could see it?

apeZ · 13 Feb 2011 at 16:15

Try http://www.wolframalpha.com - might be able to integrate and show working on there.

danza · 13 Feb 2011 at 16:20

I'm trying to integrate this:

∫x^2 . e^5x dx

Wolfram doesn't like it.

I think I'll just blag it in my report and do the next bit. :/

This is for the calculus module of my Engineering HND.

skippy2421 · 13 Feb 2011 at 16:22

danza said:
I'm trying to integrate this:

∫x^2 . e^5x dx

Wolfram doesn't like it.

I think I'll just blag it in my report and do the next bit. :/

would you like me to show you? wrote some working on paper and ill scan it up for you, but like i said if you looked at integration by parts it's relatively simple

Right so it appears that the problem you have is in the second square bracket. This is how I would have integrated it.

danza · 13 Feb 2011 at 16:42

You've ignored/missed the fact that U=X^2, which is what's causing me trouble. I think.

I'll scan in what I have in a bit and show you.

skippy2421 · 13 Feb 2011 at 16:46

ermmm I haven't missed anything you asked how the first thing in your picture becomes the second. That's what I've done integrated out the second set of square brackets.

If you want ∫x^2 . e^5x dx

You use integration by parts to get the first line of what you have in your image then use my working out to give you the second line.

hold on hold on I think I might see where you have got yourself confused. You've used U=x^2 in the first part of your integration to get your first line in the image right? however when you integrate the second set of brackets U does not remain x^2 you now set it to x.