Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Relationship between f(x) and f(1/x)

  1. Feb 4, 2010 #1
    Here's a problem that I am having difficulty doing:

    1. The problem statement, all variables and given/known data
    The question states:
    if 2f(x)-3f(1/x)=x^2, determine f(2)

    I am confused about the relationship between f(x) and f(1/x). My attempt right now consists of substituting y for f(x), 1/y for f(1/x) and 2 for the x in x^2 but i am quite sure that this is wrong since I do not get the answer that I was supposed to get (which is -7/4)
  2. jcsd
  3. Feb 4, 2010 #2
    There is no relationship between f(x) and f(1/x) other then what you get from 2f(x)-3f(1/x)=x^2. if y = f(x) then 1/y would be 1/f(x) and this is not equal to f(1/x)

    You can try to substitute various values for x and see what you get

    if x = 1 this tells you that 2f(1) - 3f(1) = 1 so f(1) = -1

    if x=2 this tells you that 2f(2) - 3f(1/2) = 4

    now try to find another equation with f(2) in it
  4. Feb 5, 2010 #3
    Thank you very much for the quick response. I was able to go from where you left off and get the correct answer. :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook