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# c2 differentiation watch

1. someone help me with c2 differentiation, I dont understand it with shapes
2. Hello I've moved this to maths for you.

Could you post an example of a question you are struggling with?
3. (Original post by rayquaza17)
Hello I've moved this to maths for you.

Could you post an example of a question you are struggling with?

for example if you have a look at the edexcel june 2014 c2 paper all of question 10.

I really do not understand any of it

4. (Original post by Mr revision)
for example if you have a look at the edexcel june 2014 c2 paper all of question 10.

I really do not understand any of it

So others don't have to find the question, here's the paper:
http://qualifications.pearson.com/co...-June-2014.pdf

So starting with a), how do you work out the volume of a prism? Please post your thoughts and any working that you have done.
5. (Original post by Mr revision)
for example if you have a look at the edexcel june 2014 c2 paper all of question 10.

I really do not understand any of it

You use the relationship between an area and a volume
(which it gives as 9600cm^3)

take the area of the trapezium ((h(a+b))/2) which for this question:
a(x) = ((4x(9x+6x))/2) = 30x^2

the volume is the area * length (y) so,
y * a(x) = 9600cm^3

therefore

y = 9600cm^3/a(x) = 9600cm^3/30x^2 = 320/x^2
--------------------------------------------------------------------
surface area:
you take:
S = 2a(x) + y(6x) + y(9x) + y(4x) + y(5x)
= 60x^2 +y(24x)
= 60x^2 + (320/x^2) * (24x)
= 60x^2 + (7680/x)
---------------------------------------------------------------------
finding minimum of S (when dS/dx = 0)
---------------------------------------------------------------------
you can justify it's a minimum if S'' is positive (>0) for the value of S you found in 10 (c)

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