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

    6
    ReputationRep:
    "f(x) = 2x + c
    g(x) = cx + 5
    fg(x) = 6x + d
    c and d are constants.
    Work out the value of d. "

    I've done the first two steps to get to 2cx+10+c... but I'm not quite sure what to do next. I'm guessing you make that equal to 6x+d but I don't know what to do after that.

    Help would be appreciated, cheers.
    • Political Ambassador
    Offline

    15
    ReputationRep:
    I recognise this as a MyMaths question.

    Think of it more simply...

    6 = 2 * ?

    Then, once you have worked out the value of c - work out fully the function fg(x) or f(g(x)).

    Then compare your equation to the equation given for fg(x) as equal and work out for the missing constant.
    • Political Ambassador
    Offline

    15
    ReputationRep:
    Or, to put it another way, you have already worked out 2cx + 10 + c...

    Thus,

    2cx + 10 + c = 6x + d

    What must c be if x is not manipulated in any other term?
    • Thread Starter
    Offline

    6
    ReputationRep:
    (Original post by ns_2)
    Or, to put it another way, you have already worked out 2cx + 10 + c...

    Thus,

    2cx + 10 + c = 6x + d

    What must c be if x is not manipulated in any other term?
    To be very honest with you, I do not know. I can't think of any method to work that out. Could you cancel out the x's?

    I'm not sure what you mean by x not being manipulated by any other term; I didn't know you could use the word "manipulated" in a mathematical context!

    Thank you for the help thus far.
    • Political Ambassador
    Offline

    15
    ReputationRep:
    (Original post by anonymous_1947)
    To be very honest with you, I do not know. I can't think of any method to work that out. Could you cancel out the x's?

    I'm not sure what you mean by x not being manipulated by any other term; I didn't know you could use the word "manipulated" in a mathematical context!

    Thank you for the help thus far.
    The only thing/term that has x in your equation is 2cx

    No other bit has x.

    On the provided equation, the only term of x is 6x.

    Hence,

    2cx must equal 6x

    And 10 + c must equal d
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    6
    ReputationRep:
    (Original post by ns_2)
    The only thing/term that has x in your equation is 2cx

    No other bit has x.

    On the provided equation, the only term of x is 6x.

    Hence,

    2cx must equal 6x

    And 10 + c must equal d
    Thank you so much!
    • Political Ambassador
    Offline

    15
    ReputationRep:
    (Original post by anonymous_1947)
    Thank you so much!
    No problem and good luck
    Posted on the TSR App. Download from Apple or Google Play
 
 
 
  • 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
    Will you be richer or poorer than your parents?
    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.