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# Logarithmic differentiation watch

1. Compute the derivative

Let

Then using logarithmic differentiation let

which equals ? I'm a bit lost now, did I miss something? Wolfram is giving me a different answer...
2. (Original post by AishaGirl)
Compute the derivative
The expressions will be equivalent, you're answer is correct.
3. (Original post by B_9710)
The expressions will be equivalent, you're answer is correct.
My answer? I've not even finished differentiating yet. I must be missing something because when I try to get rid of the square brackets it's wrong.
4. (Original post by AishaGirl)
My answer? I've not even finished differentiating yet. I must be missing something because when I try to get rid of the square brackets it's wrong.
You have finished the differentiation part - next it's just algebra. It's not wrong, I checked your answer and it's correct, it's must just be in a different form to the 'correct' answer that you saw.
5. (Original post by B_9710)
You have finished the differentiation part - next it's just algebra. It's not wrong, I checked your answer and it's correct, it's must just be in a different form to the 'correct' answer that you saw.
Wolfram alpha says that it's for where is this coming from? Is it or ?

I'm so confused. I've missed something and I think you have too?
6. Oh I have!

It's
which gives

and finally

which now matches what wolfram alpha says.

I was missing a power.
7. (Original post by AishaGirl)
Oh I have!

It's
which gives

and finally

which now matches what wolfram alpha says.

I was missing a power.
Right. I did notice you forgot the power of 2 of that term but I forgot to mention it - it was of course all right apart from that as you said.
8. Is logarithmic differentiation useful in A level? Or is this uni?
9. (Original post by thekidwhogames)
Is logarithmic differentiation useful in A level? Or is this uni?
it's useful for A2 Maths in C3, C4 and DE for MEI maths, dk about other boards though
10. (Original post by thekidwhogames)
Is logarithmic differentiation useful in A level? Or is this uni?
no need for the bump but yeah applying log to both sides can be useful at A-level to avoid getting lost in a mess of algebra
11. (Original post by _gcx)
no need for the bump but yeah applying log to both sides can be useful at A-level to avoid getting lost in a mess of algebra
Alright, thanks!
12. (Original post by NishatM)
it's useful for A2 Maths in C3, C4 and DE for MEI maths, dk about other boards though
Yeah sorry about that. I was watching a video by Prof Leonard and he went over this so it seemed to be really useful. Thanks for the help!

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