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Edexcel C3,C4 June 2013 Thread

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Original post by cooldudeman
Sometimes I honestly get a negative answer for integration and I know I have done it correctly. Do I just make it positive?

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If you were integrating to find the area, then yes, make it positive. If, for example, the area is underneath the x-axis, integrating the function will give you a negative answer.
Reply 5061
Someone diffrentiate x = e^t with respect to y

If you sucessfully do that then find d^2y/dx^2
Original post by MedMed12
haha good one!!
Good :smile: I like c4 :biggrin: :biggrin: just so tired
wbu?


I prefer C4 to C3 in terms of the syllabus, but I just know that I'll end up making a minor cock up on a few parts as always. It's annoying because the maths isn't anywhere near as hard as some make out, but I always mess up in exam situations!
Reply 5063
Original post by cooldudeman
Sometimes I honestly get a negative answer for integration and I know I have done it correctly. Do I just make it positive?

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If you have to work out area or volume it has to be positive. Though if your not asked to work out area/ volume i guess you can just leave it as a negative.


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Reply 5064
Original post by Chekz
Someone diffrentiate x = e^t with respect to y

If you sucessfully do that then find d^2y/dx^2


You've either written your variables incorrectly, or that's an almost nonsensical question.
Reply 5066
Original post by Chekz
Someone diffrentiate x = e^t with respect to y

If you sucessfully do that then find d^2y/dx^2


It's the same you get e^t when you differentiate


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What's the derivative of ex2e^{x^2} ?
Reply 5068
please can anybody solve that for me sinx^2cosx^2 ?? Integration?????
Reply 5069
Original post by help-me333
Hi guys, i'm ready for this exam but theres one thing that always trips me. When solving differential equations, what side do you gather constants on? E.G dx/dt=15(5x-1) ...do you re-arrange to 1/15(5x-1) dx=dt

or 1/(5x-1) dx = 15dt

do the second because then you can bring dt over to the other side.
(edited 10 years ago)
Reply 5070
Reply 5071
Original post by fahmad1
please can anybody solve that for me sinx^2cosx^2 ?? Integration?????

sin2xcos2x=(12sin2x)2sin^2xcos^2x =( \frac{1}{2}sin2x )^2 now expand the brackets and integrate.
Original post by orange94
Integrate by parts



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Good luck integrating ex2e^{x^2}.


y=ex2y = e^{x^2}

lny=lnex2\ln y = \ln e^{x^2}

lny=x2\ln y = x^2

Differentiating both sides w.r.t x:

1y×dydx=2x\dfrac{1}{y} \times \dfrac{dy}{dx} = 2x

dydx=2xy=2xex2\dfrac{dy}{dx} = 2xy = 2xe^{x^2}


Does this help you figure out how to integrate that?
A quick question, on mixed exercise 6L question 34)d) ? how
Reply 5075
Original post by nm786
do the second because then you can bring dt over to the other side.


Could you expand and then do it?
Reply 5076
Original post by nm786
sin2xcos2x=(12sin2x)2sin^2xcos^2x =( \frac{1}{2}sin2x )^2 now expand the brackets and integrate.


Would you integrate that by reverse chain rule


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Reply 5077
Original post by OneMorePanda
What's the derivative of ex2e^{x^2} ?



Original post by orange94
Integrate by parts



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Book shows to integrate by substitution but I'm lost.
Original post by OneMorePanda
Good luck integrating ex2e^{x^2}.
Original post by OneMorePanda
Good luck integrating ex2e^{x^2}.


Isn't that just (1/2x) e^x^2 ? :s


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Reply 5079
Original post by Story
Could you expand and then do it?

no don't expand it.
(edited 10 years ago)

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