You are Here: Home >< Maths

# C3 Differentation - TAKES TWO SECS watch

Announcements
1. My notes are 'patchy' at best...

Could someone tell me if this is correct please.

y = 3/x dy/dx = 3lnx

y= 1/3x dy/dx = ln3x
2. No, you've integrated.

y=3/x means y = 3x-1
Differentiate that and you get dy/dx = -3x-2

Well, you've integrated for the first one. You've done something very weird for the second one!
3. no....if y=3lnx....dy/dx will be 3/x

if y=ln3x dy/dx=1/3x....you've got it the wrong way round!
4. (Original post by christina.s)
no....if y=3lnx....dy/dx will be 3/x

if y=ln3x dy/dx=1/3x....you've got it the wrong way round!
If Y = ln3x , I thought dy/dx = 1/x

as ln3x can be ln3+lnx..

ln3 is just a number

so you just differentiate lnx = 1/x
5. Balls.

Thanks for that. Is what i posted originally correct in terms of integration?
6. (Original post by Jimi Haze)
If Y = ln3x , I thought dy/dx = 1/x

as ln3x can be ln3+lnx..

ln3 is just a number

so you just differentiate lnx = 1/x

yeh....you're right!!!i really shouldnt be taking my c3exam on thursday!
7. You've got problems? Mine's tomorrow morning.
8. Did anyone else read the title and expect this topic to involve some hilariously bad pun?
9. Indeed, d(ln3x)/d(x)=1/x, because differentiating ln (f(x)) gives f'(x)/f(x). If f(x)=3x, f'(x)=3, so dy/dx = 3/3x=1/x.
10. (Original post by ILoveDrugs)
You've got problems? Mine's tomorrow morning.
Likewise.
Eeek!
11. (Original post by Fointy)
Did anyone else read the title and expect this topic to involve some hilariously bad pun?
Haha, shamefully, yes!!!
12. (Original post by Fointy)
Did anyone else read the title and expect this topic to involve some hilariously bad pun?
YES! I was quite disappointed
13. i thought that if you differentiate y=ln3x you'd get 3/3x
14. (Original post by Fointy)
Did anyone else read the title and expect this topic to involve some hilariously bad pun?
Yes - and i was going to reply with something like 'actually that took me two cosecs'... sorta had the edge taken out of it now.
15. (Original post by DominF)
i thought that if you differentiate y=ln3x you'd get 3/3x
Indeed, that's what I make it!
16. Isn't 3/3x the same as 1/x or should i just give up now?
17. (Original post by ILoveDrugs)
Isn't 3/3x the same as 1/x or should i just give up now?
Ahahaha! SO it is!
Perhaps I should give up!
This is why I'm applying for English at uni! Damn maths!
18. don't worry, it is :P i find the best way is to just consider that if

y = ln f(x)

then dy/dx = f'(x)/f(x)
19. (Original post by Fointy)
Did anyone else read the title and expect this topic to involve some hilariously bad pun?
unfortunately
20. (Original post by Fointy)
Did anyone else read the title and expect this topic to involve some hilariously bad pun?
"This is the problem: differentiate 2/cosx"

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: January 11, 2008
Today on TSR

### Lied on my UCAS

And my school told me not to change it

### University open days

• University of the West of England, Bristol
Wed, 23 Jan '19
• University of East London
Wed, 23 Jan '19
• University of Gloucestershire
School of Education Open Day Postgraduate
Wed, 23 Jan '19
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams