Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    7
    ReputationRep:
    Hello

    I am stuck on this:

    4x - 3__ __x - 3
    -------_ = _-------
    1 - 5x__ __x + 7

    (Sorry I don't know how to format it right)


    So this is what I get, I firstly get rid of the fractions =

    (4x - 3)(x + 7) = (x - 3)(1 - 5x)

    Expand it out:

    4x^2+28x-3x-21 ---> simplied too: 4x^2 +25x -21.

    x - 5x^2 - 3 - 15x ---> simplied too: -5x^2 - 14x - 3

    4x^2 + 25x - 21 = -5x^2 - 14x - 3

    Move it all to one side =

    4x^2 + 25x - 21 (+5x^2 + 14x + 3)

    9x^2 + 39x - 18

    I then try to factorise it...
    9 x - 18 = -162... but I can't seem to factorise it, so that tells me I have gone wrong somewhere.

    I know the answers are 1 and -1.

    Can anyone give me a nudge in the right direction? thank you
    • Very Important Poster
    • Welcome Squad
    Offline

    19
    ReputationRep:
    Very Important Poster
    Welcome Squad
    x - 5x^2 - 3 - 15x

    It's supposed to be 15x as -3 * -5 equal 15.
    Offline

    2
    ReputationRep:
    (Original post by Tinkletea)
    Hello

    I am stuck on this:

    4x - 3__ __x - 3
    -------_ = _-------
    1 - 5x__ __x + 7

    (Sorry I don't know how to format it right)


    So this is what I get, I firstly get rid of the fractions =

    (4x - 3)(x + 7) = (x - 3)(1 - 5x)

    Expand it out:

    4x^2+28x-3x-21 ---> simplied too: 4x^2 +25x -21.

    x - 5x^2 - 3 - 15x ---> simplied too: -5x^2 - 14x - 3

    4x^2 + 25x - 21 = -5x^2 - 14x - 3

    Move it all to one side =

    4x^2 + 25x - 21 (+5x^2 + 14x + 3)

    9x^2 + 39x - 18

    I then try to factorise it...
    9 x - 18 = -162... but I can't seem to factorise it, so that tells me I have gone wrong somewhere.

    I know the answers are 1 and -1.

    Can anyone give me a nudge in the right direction? thank you
    This part is wrong.
    Offline

    15
    ReputationRep:
    (Original post by Tinkletea)
    (x - 3)(1 - 5x)


    x - 5x^2 - 3 - 15x ---> simplied too: -5x^2 - 14x - 3
    Check this part.
    Offline

    1
    ReputationRep:
    (x - 3)(1 - 5x)
    x - 5x^2 - 3 - 15x ---> simplied too: -5x^2 - 14x - 3
    should be +15x

    EDIT: triple-ninja'd? :/
    • Thread Starter
    Offline

    7
    ReputationRep:
    (x - 3)(1 - 5x)
    x x 1 = x
    x x - 5x = -5x^2
    -3 x 1 = -3
    -3 x -5x = +15x

    = -5x^2 + 16x - 3
    Is that right, I forgot a negative x a negative is a positive oops

    so
    4x^2 + 25x - 21 (+5x^2 - 16x + 3)
    9x^2 + 9x - 18

    So 9 x -18 = -162
    -9 x 18 = -162 (-9 + 18 = 9) Oh!

    9x^2 - 9x + 18x - 18

    9x(x - 1) +18(x - 1)

    9x + 18 = 0 (-18 = 9x)
    -18 / 9 = x = -2
    x - 1 = 0 (+1 = x) = x = 1

    Obviously, gone wrong again, since the answers are -1 and 1?
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    I've just solved it and your solutions are correct (sub them into the original equation and you'll see )
    • Very Important Poster
    • Welcome Squad
    Offline

    19
    ReputationRep:
    Very Important Poster
    Welcome Squad
    Subbing in x = -1 in the original equation yields me -7/6 = -2/3 which means it is not a solution. Subbing in both x=-2 and x=1 in the original equation makes the two sides equal to each other.
    • Thread Starter
    Offline

    7
    ReputationRep:
    Not according to MyMaths

    But ill take your word from it, I can relax now I have got over that one!

    thanks all
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    What's your favourite Christmas sweets?
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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.