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**BarandaMan****Guest**

bobbym wrote:

Hi;

Can you differentiate this wrt Pi?

It is just a power rule.

So I think this would become nWYP^n-1Pi^-n+1?

Can we write that in a nicer way?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

Hi;

That is not correct but it is close. After we move all the constants to the left you are differentiating:

Please differentiate that right now.

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**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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**BarandaMan****Guest**

bobbym wrote:

Hi;

That is not correct but it is close. After we move all the constants to the left you are differentiating:

Please differentiate that right now.

That is I think -nPi^-n+1?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

Please use brackets.

What is the power rule?

Differentiate that please.

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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**BarandaMan****Guest**

bobbym wrote:

Please use brackets.

What is the power rule?

Differentiate that please.

Sorry: (-n)(Pi)^(-n+1)

Erm I do not know, I think that is just simply 2x once differentiated? Multiply across then subtract the one?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

(-n)(Pi)^(-n+1)

That is not correct. Just follow the formula.

Power rule:

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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**BarandaMan****Guest**

bobbym wrote:

(-n)(Pi)^(-n+1)

That is not correct. Just follow the formula.

Power rule:

Ok, thank you.

Is that not what I did with x^2? Differentiate it and you get 2x? because 2x^(2-1) = 2x^1 = 2x?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

Yes, you were right for x^2 but wrong for Pi^(-n) which means you are not using the power rule or you are using it incorrectly.

Now, please differentiate this using the power rule:

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**BarandaMan****Guest**

bobbym wrote:

Yes, you were right for x^2 but wrong for Pi^(-n) which means you are not using the power rule or you are using it incorrectly.

Now, please differentiate this using the power rule:

AHHHH! I get this, I think! So it is -nPi^(-n-1) and before I was adding one!?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

That is correct! You have one more part to do.

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**BarandaMan****Guest**

bobbym wrote:

That is correct! You have one more part to do.

YAY! Thank you!

SO, in whole must become, nWYP^(n-1)Pi(-n-1)? (For the bit you asked about before? )

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

nWYP^(n-1)Pi(-n-1)?

You left out an exponentiation sign in there.

It is Pi^(-n-1).

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**BarandaMan****Guest**

Ah yes thank you bobby, sleep eyes.

Now this term is complete? But when you posted a solution, you had (nWY((Pi/P)^(-n-1)))/P^2 ? How did you get from the differentiated thing to this for this specific term?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

There is one more term to be differentiated. When we simplify it all up we will see.

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**BarandaMan****Guest**

Ok great! Now the last term, want to differentiate (YPi((Pi/P))^(-n))/P. So for this I get (-nYPi(Pi/P)^(-n-1))/P, but I know this is wrong because there are two Pi's and I am only doing one of them, how does this work??

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

Hi;

We are not done yet, not by a long shot. Which term are we working on?

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**BarandaMan****Guest**

The last term!

I think when we differentiate it we get (-nYPi((Pi/P)^(-n-1)))/P?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

The third term has a P in the denominator. I left it out because we concentrated on the numerator. So we are not done with the third term.

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**BarandaMan****Guest**

bobbym wrote:

The third term has a P in the denominator. I left it out because we concentrated on the numerator. So we are not done with the third term.

I see, apologies for not making this clear: P and Pi are completely different things.... P could be Y or X for example! It just happens to represent something beginning with P! But Pi is what we want to differentiate with respect to!

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

We differentiated that when the real problem is this:

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**BarandaMan****Guest**

OH, so hwo do we do it?

oh my god why is this so difficult for such a little step, can we please go through this.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

Since the P is a constant just take the answer you got and put it over P.

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**BarandaMan****Guest**

bobbym wrote:

Since the P is a constant just take the answer you got and put it over P.

Ok now I am just getting confused, so that answer I had was correct?

Ok let's just leave this I don't think I can solve this problem anymore. Thank you though.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,580

Hi;

Okay, but we are almost done with the whole problem and are done with the third term.

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**BarandaMan****Guest**

Is there anyone here who can actually help me by explaining this methodically and quickly?

I have exams approaching in January and tried to solve this problem weeks ago. I cannot do it. I do not have the time to spend another 2 weeks trying to be directed to a correct answer. I have memorised the solution so that will be fine (solution is posted), but I do not understand how to differentiate it. Please help me.