Help with this differentiation question!! Watch

NickyConfused
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Edexcel C3 review 4 question 18 (Page 119)

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If you guys could explain your method, that would really help!
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Mr M
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(Original post by NickyConfused)
Edexcel C3 review 4 question 18 (Page 119)

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If you guys could explain your method, that would really help!
As it's your question - why don't you explain YOUR method. We'll let you know if you are on the right lines.
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NickyConfused
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(Original post by Mr M)
As it's your question - why don't you explain YOUR method. We'll let you know if you are on the right lines.
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I know this is wrong but I don't know WHY
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Mr M
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(Original post by NickyConfused)
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I know this is wrong but I don't know WHY
See - that answered the question in one go.

You are using the product rule on something that is not a product.
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TenOfThem
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(Original post by NickyConfused)
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I know this is wrong but I don't know WHY
It is fine until the circled bit where you suddenly seem to have used the product rule for no reason
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Kvothe the Arcane
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(Original post by TenOfThem)
It is fine until the circled bit where you suddenly seem to have used the product rule for no reason
I'm sure they had a reason. Just a wrong one
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TenOfThem
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(Original post by keromedic)
I'm sure they had a reason. Just a wrong one
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NickyConfused
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(Original post by Mr M)
See - that answered the question in one go.

You are using the product rule on something that is not a product.
I answered the question?

But I haven't gotten the final form of the answer and I don't know how to go about it. How do you even get 2(x+1)??
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Mr M
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(Original post by NickyConfused)
I answered the question?

But I haven't gotten the final form of the answer and I don't know how to go about it. How do you even get 2(x+1)??
Did you even read what we put? You used the product rule on something that is not a product. Don't do that, just differentiate term by term.

\displaystyle \frac{d}{dx} (ax+b)^n = an (ax+b)^{(n-1)}
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TenOfThem
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(Original post by NickyConfused)
I answered the question?

But I haven't gotten the final form of the answer and I don't know how to go about it. How do you even get 2(x+1)??

Why have you used uv' + u'v
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NickyConfused
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(Original post by Mr M)
Did you even read what we put? You used the product rule on something that is not a product. Don't do that, just differentiate term by term.

\displaystyle \frac{d}{dx} (ax+b)^n = an (ax+b)^{(n-1)}
I did read it, I know not to use the product rule now but how does

(2x+3)-1/2 + (2x+3)-3/2= Given answer from txtbook ?
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NickyConfused
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(Original post by TenOfThem)
Why have you used uv' + u'v
it still gives the same answer i swear?
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TenOfThem
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(Original post by NickyConfused)
it still gives the same answer i swear?
Swear all you want

It doesn't

Why would it
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Mr M
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(Original post by NickyConfused)
I did read it, I know not to use the product rule now but how does

(2x+3)-1/2 + (2x+3)-3/2= Given answer from txtbook ?
You need to add the fractions. This means you should find a common denominator.
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TenOfThem
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(Original post by NickyConfused)
I did read it, I know not to use the product rule now but how does

(2x+3)-1/2 + (2x+3)-3/2= Given answer from txtbook ?
Write it as fractions

Add your fractions
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NickyConfused
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(Original post by Mr M)
You need to add the fractions. This means you should find a common denominator.
this is where I get stuck. Do I cube the (2x+3)-1/2​ ?
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Kvothe the Arcane
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(Original post by NickyConfused)
this is where I get stuck. Do I cube the (2x+3)-1/2​ ?
I'm a bit late to the thread but why don't you take out the smaller factor (2x+3)^{\frac{-1}{2}}?

And then use the property that f(x)^n+f(x)^m=f(x)^n(1+f(x)^{m-n}),n<m
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TenOfThem
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(Original post by NickyConfused)
this is where I get stuck. Do I cube the (2x+3)-1/2​ ?
Why would you want to cube it

Can you do this question

\dfrac{1}{3} + \dfrac{1}{27}

Or this question

\dfrac{1}{a} + \dfrac{1}{a^3}
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Mr M
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(Original post by keromedic)
I'm a bit late to the thread but why don't you take out the smaller factor (2x+3)^{\frac{-1}{2}}?

And then use the property that f(x)^n+f(x)^m=f(x)^n(1+f(x)^{m-n}),n<m
I can tell you are not a teacher. That isn't pitched at an appropriate level I'm afraid!
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Mr M
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(Original post by NickyConfused)
this is where I get stuck. Do I cube the (2x+3)-1/2​ ?
TenOfThem is leading you through this step. Listen to her.
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