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

    2
    ReputationRep:
    f(x)=3(2^-x)-1
    The function g is g(x)=\log_2 x
    Find fg(x), giving your answer in its simplest form.

    Okay, the answer is supposed to be \frac{3}{x}-1

    What I've done so far
    f(\log_2 x )=3( 2^\-log_2 x ) -1
    (The log has a minus in front of it but I don't know how to get that to work in Latex)

    =3(2^\log_2 x^-1) -1
    Not sure how to get it in the form needed
    Offline

    17
    ReputationRep:
    (Original post by mintmocha)
    f(x)=3(2^-x)-1
    The function g is g(x)=\log_2 x
    Find fg(x), giving your answer in its simplest form.

    Okay, the answer is supposed to be \frac{3}{x}-1

    What I've done so far


    Not sure how to get it in the form needed
    Note that a^{\log _a k} = k. In your case, a=2 and k=...
    Offline

    2
    ReputationRep:
    2^log_2 (x^-1)=x^-1
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Farhan.Hanif93)
    Note that a^{\log _a k} = k. In your case, a=2 and k=...
    Ah, thank you!
    I didn't know about this rule.
 
 
 
  • 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
    Has a teacher ever helped you cheat?
    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

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