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Integration help

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Reply 1
Original post by SuperiorGenius


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I don't understand what "find an expression for y in terms of x" means.
Reply 3
What exactly do you want help with?
Reply 4
Original post by SuperiorGenius
I don't understand what "find an expression for y in terms of x" means.


y = x basically. it's given you dy/dx so to get back to y = x... you integrate..
Reply 5
Original post by SuperiorGenius
I don't understand what "find an expression for y in terms of x" means.


e.g. y = 3x2 +7x
Original post by Blobar
y = x basically. it's given you dy/dx so to get back to y = x... you integrate..

So what do I do with the numbers y=5 and x=1?
Original post by SuperiorGenius
So what do I do with the numbers y=5 and x=1?


Have you learnt how to integrate?

Do you understand about the constant of integration?

If you know a point on the curve for example (1,5) then you can find the value of c
Reply 8
Original post by SuperiorGenius
So what do I do with the numbers y=5 and x=1?


What did you get when you integrated 2x + 1.
Original post by Blobar
What did you get when you integrated 2x + 1.

x^2+1x
Reply 10
Original post by SuperiorGenius
x^2+1x


Yes but unless you are finding a general solution there is an integration constant which you've missed out, it is essential to know that for this question.
Original post by Blobar
Yes but unless you are finding a general solution there is an integration constant which you've missed out, it is essential to know that for this question.

So how would you work out the constant with the y=5 and x=1?
Reply 12
Original post by SuperiorGenius
So how would you work out the constant with the y=5 and x=1?


So you'll have y = x^2 + x + c.

Put the numbers in and see what you get for c.
Original post by Blobar
So you'll have y = x^2 + x + c.

Put the numbers in and see what you get for c.

Oh ****. I feel like a retard now. Thanks.
Reply 14
Original post by SuperiorGenius
Oh ****. I feel like a retard now. Thanks.


Yeah no problem man, you can always miss the easiest of things.
Original post by Blobar
y = x basically. it's given you dy/dx so to get back to y = x... you integrate..

I think he means once you've integrated, you need an exact expression... meaning use the supplied values to work out what the constant of integration, C, is.

Pretty straightforward, I think. :smile:

edit: yeah that was right. unless you're doing integration between boundaries, remember the constant C.
(edited 9 years ago)
Original post by spotify95
I think he means once you've integrated, you need an exact expression... meaning use the supplied values to work out what the constant of integration, C, is.

Pretty straightforward, I think. :smile:

edit: yeah that was right. unless you're doing integration between boundaries, remember the constant C.

The Curve C with equation y=f(x) is such that
dy/dx=3x^2 + kx
k=constant
Given that C passes through the points (1,6) and (2,1)
- find value of K
-Find equation of the curve.
Don't know where to start
Original post by SuperiorGenius
The Curve C with equation y=f(x) is such that
dy/dx=3x^2 + kx
k=constant
Given that C passes through the points (1,6) and (2,1)
- find value of K
-Find equation of the curve.
Don't know where to start


Integrate to find an equation for y in terms of x with two unknown constants k and c. Now substitute the points you were given to find the values of those constants.
Original post by SuperiorGenius
The Curve C with equation y=f(x) is such that
dy/dx=3x^2 + kx
k=constant
Given that C passes through the points (1,6) and (2,1)
- find value of K
-Find equation of the curve.
Don't know where to start

hmmm.... that's a bit of a tough cookie :biggrin: I'll get back to you on it :wink:
Original post by Mr M
Integrate to find an equation for y in terms of x with two unknown constants k and c. Now substitute the points you were given to find the values of those constants.

I've integrated it at y=x^3+0.5kx^2+c. Now do I set up simultaneous equations to solve?

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