Join TSR now and get all your revision questions answeredSign up now

Partial fractions from a single fraction? Watch

    • Thread Starter
    Offline

    2
    ReputationRep:
    I've just started to study this and I'm stuck as hell on a question in my text book. I cannot for the life of me see how they get the answer they do. Can someone please explain the procedure?

    The algebraic fraction is:

    3x+9 / x2 + 8x + 12

    When I work this out I get partial fractions of:

    0.75 / x+2 + -0.25 / x+6 (the numerators are fractions themselves)

    The answer given in the book is:

    1/4 (3/x+2 + 9/x+6)


    Oh... and can someone point me towards a tutorial for writing mathematical formula, fractions etc. correctly please? I know there's one on here somewhere but I can't find it now.
    • Community Assistant
    • Welcome Squad
    Offline

    3
    ReputationRep:
    (Original post by Darwinion)
    I've just started to study this and I'm stuck as hell on a question in my text book. I cannot for the life of me see how they get the answer they do. Can someone please explain the procedure?

    The algebraic fraction is:

    3x+9 / x2 + 8x + 12

    When I work this out I get partial fractions of:

    0.75 / x+2 + -0.25 / x+6 (the numerators are fractions themselves)

    The answer given in the book is:

    1/4 (3/x+2 + 9/x+6)


    Oh... and can someone point me towards a tutorial for writing mathematical formula, fractions etc. correctly please? I know there's one on here somewhere but I can't find it now.
    Well you've got the first fraction right anyway, so I assume you're making a mistake at some point when it comes to finding the numerator of the other fraction.

    \displaystyle \frac{3x+9}{x^2+8x+12}=\frac{3x+  9}{(x+2)(x+6)}= \frac{A}{x+2}+ \frac{B}{x+6}=\frac{Ax+6A+Bx+2B}  {(x+2)(x+6)}

    Means Ax+Bx=3x and 6A+2B=9

    And since you know that A=\frac{3}{4} then you can find B since you know that B=3-A from eq 1


    http://www.thestudentroom.co.uk/wiki/LaTex
    • Thread Starter
    Offline

    2
    ReputationRep:
    Thanks for that! I dunno what I was doing for calculating B. The way you laid it out quite clearly shows that B=2\frac{1}{4}

    Yay... and I got the LaTex right That's gonna need some practice though.
 
 
 
Poll
Is GoT overrated?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.