C4 Differentiating by quotient rule, I'm stuck Watch

Sayless
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I'm stuck on the following question:

Question bi), I need to differentiate N basically, I went for the quotient rule to do this, here is my working:


I kind of got it but the minus is the wrong way around. I have checked my working multiple times, went to sleep woke up and did the question again, each time getting the same answer. However, when I do chain rule I get the right answer, quotient rule should work on this I think but it's not working for me, help would be appreciated, thanks
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Dinaa
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I this thread thinking yh cool i'm really good at differentiating :lol:
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Student403
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Over here when you applied the quotient rule, it should have been "0 - that" which would have turned that numerator positive.
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Sayless
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(Original post by Student403)


Over here when you applied the quotient rule, it should have been "0 - that" which would have turned that numerator positive.
nice spot, thanks man
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Zacken
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(Original post by Sayless)
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The quotient rule is: \displaystyle \frac{ \mathrm{d} }{ \mathrm{d}x } \frac{u}{v} = \frac{v \frac{du}{dx} -  u \frac{dv}{dx}}{v^2}

In this case, your numerator should be \displaystyle v(0) - 500\left(-\frac{9}{8}e^{-t/8}\right), look at the minus sign.

Oh - and don't use the quotient rule in problems like these, the chain rule is much more effective.
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Student403
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(Original post by Sayless)
nice spot, thanks man
All good

I'm glad you were persistent on this because you couldn't realise why it wasn't working instead of just doing what many people would do and going "oh that's okay I'll just accept the chain rule method". Good trait to have
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Zacken
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(Original post by Student403)

Over here when you applied the quotient rule, it should have been "0 - that" which would have turned that numerator positive.
:shakecane:
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Student403
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(Original post by Zacken)
:shakecane:
You're still up

8.5/12 is it?
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Zacken
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(Original post by Student403)
You're still up

8.5/12 is it?
Getting too old for this :laugh:
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