# quick maths question - integration

Discussion in 'General Discussion' started by dean_ham, 8 May 2006.

1. dean_ham

# Location: S.Wales

im having a blank moment here, and i have no answers...

if i intergrate 2/x, do you take the x up so its 2x^-1, then integration that will make it 2x^0 / 0, which will make it 0?

cheers

2. Dave

# Location: Sacramento CA

Nope.

The integral of 2/x dx is 2lnx.

The integral of a 1/x function, or f'(x)/f(x) is lnx, and not a constant.

edit/ don't forget the "test" by deriving your result; d/dx(2lnx) = (2)(1/x) = 2/x, so it's right. d/dx(0) . . .

3. Nitefly

# Posts: 33,379

Yep, 1/x always becomes lnx

So 10/x would be 10lnx etc.

4. dean_ham

# Location: S.Wales

cheers i looked at 1/x on my tables of intergrals, but thought nahhh lol

Thanks

as u can see i need a new maths teacher ha ha or a bit more revising

5. spirit

# Posts: 1,885

good luck with p2/3

6. Vonhelmet

# Location: On the hoods

Not to mention degree level calculus

7. spirit

8. McDaniel

# Location: Southend-on-Sea

i hated those exams with a passion

9. spirit

# Posts: 1,885

lol i only really disliked p5 'cause u actually had to think about stuff, but it was fun i guess really

10. McDaniel

# Location: Southend-on-Sea

i didnt have P5 \0/

I enjoyed maths until a-level but i did have possible the worst teacher in the world, who got her own calculations wrong and the class had to correct her

11. spirit

# Posts: 1,885

fair enough my alevel teacher for pure was weird - he was some kind of maths genius (in terms of like olympiad questions and stuff) but would always get stuff like basic alevel integration wrong lol but he taught us alot of tricks..
He also creeped me out, cause he used to put music on whilst doing maths and dance (he is gay) and it was wierd really wierd.

12. McDaniel

# Location: Southend-on-Sea

Sounds Hilarious tho

# Location: Cambridge

Eh?

My tip when doing integrations: remember that differentiation is always, ALWAYS easier than integration. You can differentiate practically anything, but some things are a complete pain in the arse to integrate.

What's the moral of this? When you've just done a tricky integration, take 20 seconds out to differentiate your answer and see if you get what you started with. It's such a simple check to make, but so many people get integrations wrong without noticing it because they don't check their answer afterwards.

If anyone saves some marks in an exam because of this, you can send money to my Paypal address.

14. spirit

# Posts: 1,885

on the same vein if you simply cant see a way to integrate (esp with ** p123 type questions) think of a something you differentiate to get that result {may not work if they use trickery with trig identities }...

not sure if that made sense or will be useful to anyone

15. Vonhelmet

N/m.