Cheers, the thing is I completely understand the chain rule but I get confused with using it with logs :\

Can anyone show how to get the answer to my question?

Reply 7

TenOfThem

18

Original post by boromir9111

I +repped to restore JUSTICE to f38 :awesome:

ta

Reply 8

boromir9111

17

Original post by oj234

Cheers, the thing is I completely understand the chain rule but I get confused with using it with logs :\

Can anyone show how to get the answer to my question?

Same rule applies to log questions. You treat what's inside the brackets as a variable.

So, f(x) = log(2x+3).

Let, 2x+3 = y.

Log(y) = f(x).....

make any sense?

Reply 9

TenOfThem

18

Original post by oj234

Cheers, the thing is I completely understand the chain rule but I get confused with using it with logs :\

Can anyone show how to get the answer to my question?

what is

\dfrac{d}{du} lnu

what is

\dfrac{d}{dx} (x+5)^3

OP

nobody?

Original post by oj234

nobody?

lol you are funny

did you even look at posts 9&10

Reply 12

oj234

OP

1

Original post by TenOfThem

lol you are funny

did you even look at posts 9&10

Hilarious

Look I completely understand the chain/log rule.

For example 79 + ln(5x-25)+ln(9-x) differentiated = 1/(5x-25) (5) + 1/(9-x)(-1)

= 5/5x-25 - 1/9-x

=1/x-5 - 1/9-x

... but it's that exact question I posted that I dont understand because of the indices...so instead of being patronising and acting like you know all, why not work us through and show us how you got the answer? :smile:

kthanks.

Reply 13

oj234

OP

1

Original post by lemollient_naw

I'm not sure quite what the politics are for responding to TSR maths threads, but since it's a single problem and you're confused, I don't see any harm in doing it for you.

d/dx(ln70 + ln(x+5)^3 - ln(14-2x))
= d/dx(ln70 + 3ln(x+5) - ln(14-2x))
= 3/(x+5) - 2/(14-2x)

Then simplify and turn into a single fraction.

Thanks thats all I asked for :smile:

Reply 14

TenOfThem

18

Original post by oj234

Hilarious

Look I completely understand the chain/log rule.

For example 79 + ln(5x-25)+ln(9-x) differentiated = 1/(5x-25) (5) + 1/(9-x)(-1)

= 5/5x-25 - 1/9-x

=1/x-5 - 1/9-x

... but it's that exact question I posted that I dont understand because of the indices...so instead of being patronising and acting like you know all, why not work us through and show us how you got the answer? :smile:

kthanks.

You know, after the neg I gave you the benefit of the doubt because you are at Manchester

However ... you are now simply being rude

Both myself and Boromir showed you how to approach this question ... the polite response would be to quote either post 9 or post 10 and say ... I understand blah but not blah

Reply 15

oj234

OP

1

Original post by TenOfThem

You know, after the neg I gave you the benefit of the doubt because you are at Manchester

However ... you are now simply being rude

Both myself and Boromir showed you how to approach this question ... the polite response would be to quote either post 9 or post 10 and say ... I understand blah but not blah

So you've been stalking me, cool :smile:

What you should have done is answer the question like the poster above you, or not answered at all.

x

Reply 16

TenOfThem

18

Original post by lemollient_naw

I'm not sure quite what the politics are for responding to TSR maths threads, but since it's a single problem and you're confused, I don't see any harm in doing it for you.

d/dx(ln70 + ln(x+5)^3 - ln(14-2x))
= d/dx(ln70 + 3ln(x+5) - ln(14-2x))
= 3/(x+5) - 2/(14-2x)

Then simplify and turn into a single fraction.

the "politics" are explained here

http://www.thestudentroom.co.uk/showthread.php?t=403989

Reply 17

TenOfThem

18

Original post by oj234

So you've been stalking me, cool :smile:

What you should have done is answer the question like the poster above you, or not answered at all.

x

Hardly stalking

It was clear that you are not a regular maths poster so I had a look to see why you might be posting

Realising that you are an under-grad who was stuck encouraged me to come back and help

You clearly wanted just the answer rather than any understanding ... since I am a follower of the guidelines that was not going to happen