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

    0
    ReputationRep:
    Ok well I am having trouble understanding linear functions and how exactly they should be solved... for example

    3(x-1) -4(x-2) -6(2x+3) =0

    the answer to this is -1 but I dont get how its arrived at this
    I know all about multiplying out the brackets first and then I believe you subtract from the RHS if its added on the LHS but some of the examples I am doing dont seem to add up?? Like sometimes they are adding when i feel they should be suntracting on the RHS??? I am soo confused. Can anyone do a step by step of the above for me fully explaining because i have spent hours on this and i am not gettin it at all.. dont know whats wrong with me!! Stressed out!! My exam is on the 10th Jan and I am feeling really out of my depth!!
    Offline

    14
    ReputationRep:
    First step here is multiply out the brackets. What do you get?
    • Thread Starter
    Offline

    0
    ReputationRep:
    3x -3-4x-8-12x+18=0???
    Offline

    0
    ReputationRep:
    3(x-1) -4(x-2) -6(2x+3) =0
    3x-3-4x+8-12x-18=0 multiply brackets out
    -13x-13=0 collect 'like' terms
    -13=13x rearrange to get 'x' on one side
    -1=x divide by 13 to get an answer of -1
    Offline

    0
    ReputationRep:
    (Original post by claireholt)
    3x -3-4x-8-12x+18=0???
    you should practise expanding brackets where negative numbers are involved
    • Thread Starter
    Offline

    0
    ReputationRep:
    [QUOTE=MBall1994;28966344]3(x-1) -4(x-2) -6(2x+3) =0
    3x-3-4x+8-12x-18=0 multiply brackets out
    -13x-13=0 collect 'like' terms
    -13=13x rearrange to get 'x' on one side
    -1=x divide by 13 to get an answer of -1[/QUOTE

    Right I understand most of that except the "collecting like terms" bit, how have you arrived at this?? :confused:
    Offline

    2
    ReputationRep:
    (Original post by claireholt)
    Ok well I am having trouble understanding linear functions and how exactly they should be solved... for example

    3(x-1) -4(x-2) -6(2x+3) =0

    the answer to this is -1 but I dont get how its arrived at this
    I know all about multiplying out the brackets first and then I believe you subtract from the RHS if its added on the LHS but some of the examples I am doing dont seem to add up?? Like sometimes they are adding when i feel they should be suntracting on the RHS??? I am soo confused. Can anyone do a step by step of the above for me fully explaining because i have spent hours on this and i am not gettin it at all.. dont know whats wrong with me!! Stressed out!! My exam is on the 10th Jan and I am feeling really out of my depth!!
    Here's a random example; hopefully it'll help you figure out where you're going wrong. PS, the Maths help forum is here.

    6(x+2)-3(x-7)-3(3x+2)=0

    Multiply out all the brackets:
    6(x+2) = 6x+12
    -3(x-7) = (-3) multiplied by (x-7) = -3x + 21 because two negatives (-3 and -7) multiplied together gives you a positive number.
    -3(3x+2) = (-3) multiplied by (3x+2) = -9x-6 because one negative multiplied by one positive (-3 and 2) gives you a negative number.

    So let's put this back:

    6(x+2)-3(x-7)-3(3x+2)=0
    6x+12-3x+21-9x-6=0

    Simplify this by collecting all the similar things together; in other words, group all your "x" and all your normal numbers together so it's easier to look at:

    Collecting your "x"s together, you get 6x-3x-9x, which is -6x
    Collecting numbers together, you get 12+21-6, which is 27

    So,

    -6x+27=0

    Now what you want to do is put "x" on one side, and have numbers on the other side. At the moment, you've got both of them on one side. So, one thing you can do is add 6x to both sides.

    -6x+6x+27=6x

    Because -6x+6x = 0, that is the same as
    27=6x
    So x=27/6

    Another way of thinking about this is "moving" 6x to the other side, and when you move sides, you gotta switch the sign. So negative becomes positive if you want to switch sides.
    Offline

    14
    ReputationRep:
    (Original post by claireholt)
    3x -3-4x-8-12x+18=0???
    As Pheylan says, this is not quite correct.
    Once you have it correct though, you need to, as said above, collect 'like' terms. ie if you had 3+4x+2+6x you'd get 5+10x. Can you see that?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Chelle-belle)
    Here's a random example; hopefully it'll help you figure out where you're going wrong. PS, the Maths help forum is here.

    6(x+2)-3(x-7)-3(3x+2)=0

    Multiply out all the brackets:
    6(x+2) = 6x+12
    -3(x-7) = (-3) multiplied by (x-7) = -3x + 21 because two negatives (-3 and -7) multiplied together gives you a positive number.
    -3(3x+2) = (-3) multiplied by (3x+2) = -9x-6 because one negative multiplied by one positive (-3 and 2) gives you a negative number.

    So let's put this back:

    6(x+2)-3(x-7)-3(3x+2)=0
    6x+12-3x+21-9x-6=0

    Simplify this by collecting all the similar things together; in other words, group all your "x" and all your normal numbers together so it's easier to look at:

    Collecting your "x"s together, you get 6x-3x-9x, which is -6x
    Collecting numbers together, you get 12+21-6, which is 27

    So,

    -6x+27=0

    Now what you want to do is put "x" on one side, and have numbers on the other side. At the moment, you've got both of them on one side. So, one thing you can do is add 6x to both sides.

    -6x+6x+27=6x

    Because -6x+6x = 0, that is the same as
    27=6x
    So x=27/6

    Another way of thinking about this is "moving" 6x to the other side, and when you move sides, you gotta switch the sign. So negative becomes positive if you want to switch sides.

    Yep can clearly see where I am going wrong... i've not taken into account then negative numbers and thats why its subtracting when I feel it should be adding!! Thanks soo much
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Slumpy)
    As Pheylan says, this is not quite correct.
    Once you have it correct though, you need to, as said above, collect 'like' terms. ie if you had 3+4x+2+6x you'd get 5+10x. Can you see that?
    Yeah I can see what I have been doing wrong... wished I had come on here earlier, been going over this for last few hours!! Thanks for all your help
    Offline

    2
    ReputationRep:
    (Original post by claireholt)
    Yep can clearly see where I am going wrong... i've not taken into account then negative numbers and thats why its subtracting when I feel it should be adding!! Thanks soo much
    It's okay Good luck. Feel free to PM me if you get really stuck on anything next time and i'll try to explain.
 
 
 
  • 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
    Would you like to hibernate through the winter months?
    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.