1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Inverse function

  1. Jan 27, 2005 #1
    How do I find the inverse of the following function: f(x)= -3x^2 + 6x + 2
    The answer is +/- sqrt( [2-x/3] +1 ) + 1

    I have no idea how to get that answer. I tried switching x and y and solving for x but I can't get the answer. TiA.
     
  2. jcsd
  3. Jan 27, 2005 #2
    use complete square.....
     
  4. Jan 27, 2005 #3
    I get +/- sqrt(x-5/-3) +1
     
  5. Jan 27, 2005 #4

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    Can u solve a quadratic equation???

    If so,then solve for [itex]x=x(y) [/itex] from the equation
    [tex]y=-3x^{2}+6x+2 [/tex]

    Or you can complete the square...Correctly...

    Daniel.
     
  6. Jan 27, 2005 #5
    walk me through it... completing the square, I get -3(y-1)^2 + 5 ... and I wrote the inverse of that. I just want to know what I'm doing wrong...
     
  7. Jan 27, 2005 #6
    if your answer read like +/- sqrt((x-5)/-3) +1, then your answer is completely same as the textbook answer... why do you need help?
     
  8. Jan 27, 2005 #7

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    you mean with "x" as in
    [tex] y=-3(x-1)^{2}+5 [/tex]

    Now solve for "x"...

    Daniel.
     
  9. Jan 27, 2005 #8

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Strictly speaking, f(x)= -3x2+ 6x+ 2 doesn't have an inverse!

    Set y= -3x2+ 6x+ 2 and then use the quadratic formula to solve the quadratic equation -3x2+ 6x+ (2- y)= 0. You will see a + or - in the formula. In order to get an inverse, we need to restrict the domain. Since the vertex of the parabola is (1, 0.5), if x< 1 we get one inverse (with the -) and if x> 1 we get the other.
     
  10. Jan 27, 2005 #9
    Yeah, I drew the graph... thats why I put +/- ... + is one inverse, - is the other

    ... I see that it's the same now... I dont get why they're different though... I mean I could tack on +1 -1 etc. How was the textbook answer found... (just out of curiosity)?

    TiA
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Inverse function
  1. Inverse functions (Replies: 8)

  2. Inverse function (Replies: 1)

  3. Inverse function (Replies: 4)

  4. Inverse functions (Replies: 1)

Loading...