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c4 help

can someone help differentiate ln(x/4)?
thanks
anybody out there know the answer???
help plz
Reply 3
Avatar for JTeighty
JTeighty
2
arsenal_fabregas
anybody out there know the answer???


1/x
Reply 4
Avatar for 353
353
i think that it will go to 1/4[ln(x/4)]
JTeighty
1/x

can you show me the method on how you do it
and i will definitively rep you
Reply 6
Avatar for JTeighty
JTeighty
2
353
i think that it will go to 1/4[ln(x/4)]


this is wrong. its 1/x. As ln(x/4) goes to 1/4 divided by x/4 which simplifies to 4/4x which goes to 1/x
Reply 7
Avatar for JTeighty
JTeighty
2
differenciation of lnx is derivatrive over function. So derivitive of x/4 = 1/4 and function is x/4 so answer comes to 1/x.
how is the derivative of x/4 = 1/4 did you just differentiate x and kept the 4 the same or what?
arsenal_fabregas
how is the derivative of x/4 = 1/4 did you just differentiate x and kept the 4 the same or what?


the derivative of 10x is 10
the derivative of 1x is 1
so the derivative of 0.25x is 0.25
(0.25x is obviously x/4)
Reply 10
Avatar for taylor4452
taylor4452
d/dx [ln (x/4)]

= 1/4 * 1/x/4

= 1/4 * 4/x

= 4/4x

= 1/x

so JTeighty is right
Reply 11
Avatar for spike09
spike09
one look at it and i would say 4\x but if you integrate 4\x it would be 4lnx therefore the onle way to get back to lnx/4 is by timesing it by 0.25... yes my logic sucks sorry
Reply 12
Avatar for clowe8
clowe8
spike09
one look at it and i would say 4\x but if you integrate 4\x it would be 4lnx therefore the onle way to get back to lnx/4 is by timesing it by 0.25... yes my logic sucks sorry


That's not a bad way of looking at it at all! I think that was how my maths teacher first taught me how to integrate actually.

Here's how I would look at it:

ln (x/4) is equivalent to ln x - ln 4 and the derivative of ln x is 1/x and ln 4 is just a number. So the answer is 1/x.

Of course that could be wrong but I've coincidentally got the right answer, that's dodgy maths skills for you.
Reply 13
Avatar for spike09
spike09
clowe8
That's not a bad way of looking at it at all! I think that was how my maths teacher first taught me how to integrate actually.

Here's how I would look at it:

ln (x/4) is equivalent to ln x - ln 4 and the derivative of ln x is 1/x and ln 4 is just a number. So the answer is 1/x.

Of course that could be wrong but I've coincidentally got the right answer, that's dodgy maths skills for you.


yeah, i seem to be getting better at integration further on in the course than differentiation?? quite confusing considering i couldnt integrate for jack 2 months ago haha!! but your solution seems ok to me :smile: as long as it comes with the right answer its all good!

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