Results 1 to 4 of 4

Math Help - Graph the function?

  1. #1
    Newbie
    Joined
    Apr 2009
    Posts
    5

    Lightbulb Graph the function?

    I need some help with this one. Thanks in advance

    Graph the function.

    f(x) = log3(x - 3)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member mollymcf2009's Avatar
    Joined
    Jan 2009
    From
    Charleston, SC
    Posts
    490
    Awards
    1
    Quote Originally Posted by leilani View Post
    I need some help with this one. Thanks in advance

    Graph the function.

    f(x) = log3(x - 3)
    When you are trying to graph logs, the easiest way to do it (if you can't use a graphing calculator) is to plot points.

    We know that logs are undefined for negative values of x and also for x = 0.

    For this particular problem, you should first find the domain and any asymptotes. This will help you decide what x value you should begin with when you start plugging in values.

    To find your domain, you need to put the value of the argument (x-3) > 0 and solve for x. This gives you x > 3. This is the domain of your log function.
    So you would probably want to start with x=4 to find points on your graph.

    f(4) = log_3(4-3) = log_3(1) = 0

    Now that one was easy because we know that log(1) = 0. But it gets a little trickier when we are trying logs of other numbers. Just continue plugging values in for x and plot points on your graph. Hope that helps!!
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    28
    Quote Originally Posted by leilani View Post
    I need some help with this one. Thanks in advance

    Graph the function.

    f(x) = log3(x - 3)
    Hi there

    Your equation has the general form

     f(x) = log(A(x-B))

    where B is the horizontal translation (i.e how much the function is moved left or right across the x axis) and A as a dialation factor (this effects how steep or swallow the function is).

    Your function has been moved 3 units to the right and grows at 3 times the rate.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Mar 2007
    Posts
    1,240

    Talking

    Quote Originally Posted by leilani View Post
    Graph the function: f(x) = log3(x - 3)
    You can either use the definition of logs to graph this log function, or else use the change-of-base formula to convert the function into something your calculator can graph (and for which it can provide you with plot points).

    The first way gives:

    Code:
    -------------+----------------+---------
      powers     |    function    | value of
       of 3      |    equation    |    y
    -------------+----------------+---------
    1/3 = 3^(-1) | log_3(1/3) = y |
      x = 1/3    | 1/3 = 3^y      |  y = -1
    -------------+----------------+---------
      1 = 3^(0)  |  log_3(1) = y  |
      x = 1      |  1 = 3^y       |  y =  0
    -------------+----------------+---------
      3 = 3^1    |  log_3(3) = y  |
      x = 3      |  3 = 3^y       |  y =  1
    -------------+----------------+---------
      9 = 3^2    |  log_3(9) = y  |
      x = 9      |  9 = 3^y       |  y =  2
    -------------+----------------+---------
     27 = 3^3    | log_3(27) = y  |
      x = 27     | 27 = 3^y       |  y =  3
    -------------+----------------+---------
    The second way converts "y = log_3(x)" into "y = [ln(x)]/[ln(3)]".
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Using the graph of the Function
    Posted in the Calculus Forum
    Replies: 1
    Last Post: August 3rd 2010, 09:10 PM
  2. Graph the function y =(x-1)(x-5)
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: June 6th 2010, 02:09 PM
  3. Graph of Function
    Posted in the Algebra Forum
    Replies: 1
    Last Post: March 13th 2010, 09:21 PM
  4. graph of a function
    Posted in the Discrete Math Forum
    Replies: 0
    Last Post: November 2nd 2009, 02:45 PM
  5. Replies: 2
    Last Post: August 26th 2009, 04:51 AM

Search Tags


/mathhelpforum @mathhelpforum