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C3 Differentation - TAKES TWO SECS

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

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Reply 1
Avatar for grace_
grace_
10
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! :s:
Reply 2
Avatar for christina.s
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!
Reply 3
Avatar for Jimi Haze
Jimi Haze
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
Reply 4
Avatar for ILoveCalpol
ILoveCalpol
OP
Balls.

Thanks for that. Is what i posted originally correct in terms of integration?
Reply 5
Avatar for christina.s
christina.s
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!
Reply 6
Avatar for ILoveCalpol
ILoveCalpol
OP
You've got problems? Mine's tomorrow morning.
Reply 7
Avatar for Fointy
Fointy
2
Did anyone else read the title and expect this topic to involve some hilariously bad pun?
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.
Reply 9
Avatar for Jimi Haze
Jimi Haze
ILoveDrugs
You've got problems? Mine's tomorrow morning.

Likewise.
Eeek!
Reply 10
Avatar for Queenie!
Queenie!
Fointy
Did anyone else read the title and expect this topic to involve some hilariously bad pun?


Haha, shamefully, yes!!!
Reply 11
Avatar for Lili!
Lili!
1
Fointy
Did anyone else read the title and expect this topic to involve some hilariously bad pun?


YES! I was quite disappointed :rolleyes:
Reply 12
Avatar for DominF
DominF
2
i thought that if you differentiate y=ln3x you'd get 3/3x
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. :redface:
Reply 14
Avatar for Queenie!
Queenie!
DominF
i thought that if you differentiate y=ln3x you'd get 3/3x


Indeed, that's what I make it!
Reply 15
Avatar for ILoveCalpol
ILoveCalpol
OP
Isn't 3/3x the same as 1/x or should i just give up now?
Reply 16
Avatar for Queenie!
Queenie!
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!
Reply 17
Avatar for DominF
DominF
2
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)
Reply 18
Avatar for M.A.H
M.A.H
17
Fointy
Did anyone else read the title and expect this topic to involve some hilariously bad pun?

unfortunately:p:
Reply 19
Avatar for 73337
73337
18
Fointy
Did anyone else read the title and expect this topic to involve some hilariously bad pun?


"This is the problem: differentiate 2/cosx"

:frown:

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