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# First derivative confusion watch

1. what is the first derivative of this function?

f(x) = ln70 + ln(x+5)^3 + ln(14-2x)

Thanks
2. (Original post by oj234)
what is the first derivative of this function?

f(x) = ln70 + ln(x+5)^3 + ln(14-2x)

Thanks
ln70 is just a number

For the other parts you need to use the chain rule
3. I know but still having trouble with using the chain rule - can anyone demonstrate?
4. (Original post by oj234)
I know but still having trouble with using the chain rule - can anyone demonstrate?
5. (Original post by oj234)
I know but still having trouble with using the chain rule - can anyone demonstrate?
You seriously negged me for responding to your question

WOW
6. (Original post by TenOfThem)
You seriously negged me for responding to your question

WOW
I +repped to restore JUSTICE to f38
7. 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?
8. (Original post by boromir9111)
I +repped to restore JUSTICE to f38
ta
9. (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?
10. (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

what is
11. nobody?
12. (Original post by oj234)
nobody?
lol you are funny

did you even look at posts 9&10
13. (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?

kthanks.
14. (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
15. (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?

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
16. (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

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

x
17. (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

18. (Original post by oj234)
So you've been stalking me, cool

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
19. (Original post by oj234)
what is the first derivative of this function?

f(x) = ln70 + ln(x+5)^3 + ln(14-2x)

Thanks
Spoiler:
Show

d/dx= 1/(x+5) -2/(14-2x)
20. The problem was that I forgot that ln(x)^y is simply the same as yln(x). Thank you for refreshing my memory lemollient_naw

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