The Student Room Group

Maths C4 - Partial Fractions... HELP??

So I'm stuck on part (C).
C4 EXE1E Q1.png


I have no idea how to do the long algebraic division part with this one :frown:

How do I do long algebraic division from... x3x2x3x2x \frac{x^3 - x^2 - x - 3}{x^2 - x}???
Original post by Philip-flop
So I'm stuck on part (C).
C4 EXE1E Q1.png


I have no idea how to do the long algebraic division part with this one :frown:

How do I do long algebraic division from... x3x2x3x2x \frac{x^3 - x^2 - x - 3}{x^2 - x}???


OH YES HERE WE GO!

Well attempt it first so we can see where you're going wrong :smile:
Reply 2
Original post by Philip-flop


How do I do long algebraic division from... x3x2x3x2x \frac{x^3 - x^2 - x - 3}{x^2 - x}???


It's pretty hard to explain, but this https://www.youtube.com/watch?v=JZda1TjCHlU is a good example of doing so, can you replicate the example for yours?
Original post by Philip-flop
So I'm stuck on part (C).
C4 EXE1E Q1.png


I have no idea how to do the long algebraic division part with this one :frown:

How do I do long algebraic division from... x3x2x3x2x \frac{x^3 - x^2 - x - 3}{x^2 - x}???


first, divide the first term, x^3 by x^2, then multiply with the divisor and subtract from the numerator.
Original post by RDKGames
OH YES HERE WE GO!

Well attempt it first so we can see where you're going wrong :smile:


False alarm. After having a little break I realised I was being quite silly. I managed to do the long algebraic division part so now I can move on from there and finish the rest of the question :smile:

Photo 09-12-2016, 00 28 18.jpg
Original post by Zacken
It's pretty hard to explain, but this https://www.youtube.com/watch?v=JZda1TjCHlU is a good example of doing so, can you replicate the example for yours?


Awesome video :smile: Helped a lot!!
Reply 6
Original post by Philip-flop
False alarm. After having a little break I realised I was being quite silly. I managed to do the long algebraic division part so now I can move on from there and finish the rest of the question :smile:

Photo 09-12-2016, 00 28 18.jpg


Yup! A nice way to do this without fiddly division is like so:

x3x2x3x(x1)=x2(x1)x3x(x1)=x2x(x1)x+3x(x1)=xx+3x(x1)\displaystyle \frac{x^3-x^2-x-3}{x(x-1)} = \frac{x^2(x-1) - x - 3}{x(x-1)} = \frac{x^2}{x(x-1)} - \frac{x+3}{x(x-1)} = x - \frac{x+3}{x(x-1)}

But it's just a clever parlor trick really.
Original post by Zacken
Yup! A nice way to do this without fiddly division is like so:

x3x2x3x(x1)=x2(x1)x3x(x1)=x2x(x1)x+3x(x1)=xx+3x(x1)\displaystyle \frac{x^3-x^2-x-3}{x(x-1)} = \frac{x^2(x-1) - x - 3}{x(x-1)} = \frac{x^2}{x(x-1)} - \frac{x+3}{x(x-1)} = x - \frac{x+3}{x(x-1)}

But it's just a clever parlor trick really.


Wow, that's way too advance for me. I'm not sure why I can't seem to follow that little trick :colondollar: :frown:
p.s I want your brain!! :tongue:
(edited 7 years ago)
All good so far, but isn't (x+3)/(x(x-1)) also a candidate for splitting into further partial fractions?
Ok so I'm doing a C4 past paper from January 2007 but am stuck on question 4...

I've managed to find that for part (a) the partial fraction is...

2x1(x1)(2x3)=1(x1)+4(2x3) \frac{2x-1}{(x-1)(2x-3)} = \frac{-1}{(x-1)} + \frac{4}{(2x-3)}

but I dont understand what is meant by the "general solution" bit for part (b). Does it just mean find the original equation from differential equation given?? ...

C4 Jan 2007 paper Q4.png

Can someone help me please? :frown:
(edited 7 years ago)
Original post by Philip-flop
Ok so I'm doing a C4 past paper from January 2007 but am stuck on question 4...

I've managed to find that for part (a) the partial fraction is...

2x1(x1)(2x3)=1(x1)+4(2x3) \frac{2x-1}{(x-1)(2x-3)} = \frac{-1}{(x-1)} + \frac{4}{(2x-3)}

but I dont understand what is meant by the "general solution" bit for part (b). Does it just mean find the original equation from differential equation given?? ...


Can someone help me please? :frown:


When you integrate something like 2x.dx=x2+c\displaystyle \int 2x .dx = x^2+c you get a whole family of particular solutions depending on what your constant is. By the "general" solution we are referring to x2+cx^2+c explicitly where the constant is arbitrary (and not to be forgotten about). The next part asks you to find a particular solution, and these are found only if a certain condition is given; such as y(2)=10y(2)=10 from your Q which allows you solve for the particular constant
(edited 7 years ago)
Original post by RDKGames
When you integrate something like 2x.dx=x2+c\displaystyle \int 2x .dx = x^2+c you get a whole family of particular solutions depending on what your constant is. By the "general" solution we are referring to x2+cx^2+c explicitly where the constant is arbitrary (and not to be forgotten about). The next part asks you to find a particular solution, and these are found only if a certain condition is given; such as y(2)=10y(2)=10 from your Q which allows you solve for the particular constant


Thank you @RDKGames!! That actually makes perfect sense to me now. It's amazing how easily you explain things!! :smile: :smile:

Quick Reply

Latest