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Help with this differentiation question!!

Edexcel C3 review 4 question 18 (Page 119)

photo (11).JPG

If you guys could explain your method, that would really help!

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Original post by NickyConfused
Edexcel C3 review 4 question 18 (Page 119)

photo (11).JPG

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.
Reply 2
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NickyConfused
OP
2
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.


photo (12).JPG

I know this is wrong but I don't know WHY
Original post by NickyConfused
photo (12).JPG

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.
(edited 10 years ago)
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TenOfThem
18
Original post by NickyConfused
photo (12).JPG

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
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 :tongue:
Reply 6
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TenOfThem
18
Original post by keromedic
I'm sure they had a reason. Just a wrong one :tongue:


:smile:
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NickyConfused
OP
2
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? :s-smilie:

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)??
Original post by NickyConfused
I answered the question? :s-smilie:

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.

ddx(ax+b)n=an(ax+b)(n−1)\displaystyle \frac{d}{dx} (ax+b)^n = an (ax+b)^{(n-1)}
Reply 9
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TenOfThem
18
Original post by NickyConfused
I answered the question? :s-smilie:

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
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.

ddx(ax+b)n=an(ax+b)(n−1)\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 ?
Original post by TenOfThem
Why have you used uv' + u'v


it still gives the same answer i swear?
Original post by NickyConfused
it still gives the same answer i swear?


Swear all you want

It doesn't

Why would it
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.
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
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​ ?
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)−12(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<mf(x)^n+f(x)^m=f(x)^n(1+f(x)^{m-n}),n<m
(edited 10 years ago)
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

13+127\dfrac{1}{3} + \dfrac{1}{27}

Or this question

1a+1a3\dfrac{1}{a} + \dfrac{1}{a^3}
Original post by keromedic
I'm a bit late to the thread but why don't you take out the smaller factor (2x+3)−12(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<mf(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!
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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