C4 separating variables help please
Maths and statistics discussion, revision, exam and homework help.
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C4 separating variables help pleaseHi! So the c4 exam is tomorrow, I am fairly confident about most of the topics integration and vectors etc and I can solve some differential equations but there are so many ways of separating them! In some past papers they separate the function and the number if there is one and sometimes they make it all a function and integrate 1 on the right hand side?!! WHY!
The formula in the edexcel textbook isnt really applicable ... it says to integrate 1/g(y) dy = integral of f(x) dx but this isnt how mark schemes do it.
Can somebody please explain the correct way of doing this? )': -
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Re: C4 separating variables help please(Original post by TenOfThem)
If
then the only way to do it is
I think you must be misunderstanding the MS if you think they are doing anything else
Do you have an example
I know what he's talking about, I think - when you separate the variables it's not always obvious what to keep on either side. e.g. dy/dx = 3x + 4, do you keep the 4 on the left or right?(Original post by Baljit-Padda)
Hi! So the c4 exam is tomorrow, I am fairly confident about most of the topics integration and vectors etc and I can solve some differential equations but there are so many ways of separating them! In some past papers they separate the function and the number if there is one and sometimes they make it all a function and integrate 1 on the right hand side?!! WHY!
The formula in the edexcel textbook isnt really applicable ... it says to integrate 1/g(y) dy = integral of f(x) dx but this isnt how mark schemes do it.
Can somebody please explain the correct way of doing this? )':
The answer, I'd say, is to look at what you're trying to get to and that will help you.
The principle is the same as with trig identities - there're loads of ways of doing it, but only one will lead you to the answer. -
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Re: C4 separating variables help please(Original post by TenOfThem)
If
then the only way to do it is
I think you must be misunderstanding the MS if you think they are doing anything else
Do you have an example
Well yes I understand that method and I use it too but it gives me the wrong answer. For example theres the june 2010 question on this topic. 75dh/dt = 4-5h and so dh/dt = (4-5h)/75 Now in this particular example they use the whole thing together as our g(y) but what I'm stuck on is how they identify the g(y) and f(x).
For example I would have thought the (4-5h) is g(y) and f(x) was 1/75 ): -
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Re: C4 separating variables help please(Original post by Junaid96)
I know what he's talking about, I think - when you separate the variables it's not always obvious what to keep on either side. e.g. dy/dx = 3x + 4, do you keep the 4 on the left or right?
The answer, I'd say, is to look at what you're trying to get to and that will help you.
The principle is the same as with trig identities - there're loads of ways of doing it, but only one will lead you to the answer.
gives
there are no variables to separate
You have to have f(x) x g(y) to separate -
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Re: C4 separating variables help pleaseIt can be either(Original post by Baljit-Padda)
Well yes I understand that method and I use it too but it gives me the wrong answer. For example theres the june 2010 question on this topic. 75dh/dt = 4-5h and so dh/dt = (4-5h)/75 Now in this particular example they use the whole thing together as our g(y) but what I'm stuck on is how they identify the g(y) and f(x).
For example I would have thought the (4-5h) is g(y) and f(x) was 1/75 ):
constant multipliers can go on either side -
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Re: C4 separating variables help pleaseIt can be either(Original post by Baljit-Padda)
but they integrate one over (4-5h)/75 so that they are integrating 75/(4-5h) on the left hand side and then they integrate 1 dt on the right hand side. Why is it not integrating 1/(4-5h) dh = integral 1/75 dt ?
works with
but also works with
the 3 can go either side
Sometimes it is easier to have it one side or the other but it will work either way -
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Re: C4 separating variables help pleaseyes(Original post by Baljit-Padda)
OHH well I just tried both methods and get the same answer.... So will I still get maximum marks even if my working is not exactly what is written in the markscheme?
I'm very grateful!
