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

Function ?

  1. Oct 28, 2004 #1
    how do I solve this one?
  2. jcsd
  3. Oct 28, 2004 #2
    You're going to have to supply more information about the problem. The actual question would be good.
  4. Oct 28, 2004 #3
    function inquiry question?

    this it function inquiry question?
  5. Oct 28, 2004 #4
    I don't think that is gonna help.
  6. Oct 28, 2004 #5


    User Avatar

    you want to solve for the roots of this function?

    in that case, your function is
    [tex] 0 = -2x^3 -9x^2 -60x[/tex] solving for x
    in that case, factor out x from the right hand side,
    you get [tex] x \cdot (-2x^2 -9x -60) = 0 [/tex]
    then you can use the quadratic formula to solve for x.
    x would equalt to [tex] \frac{-b \pm \sqrt{b^2 -4ac}}{2a}[/tex]
    which by pluging and chuging gives you two answer.
    The final answer would then be x = 0, [tex]r_{1}[/tex], [tex]r_{2}[/tex]

    in the case that you are attempting to simply draw it with the help of calculus, i do not see where the problem lies. Simply take the first derivative, set it to 0, and continue normally. perhaps a little more information on what your desired answer is...?
  7. Oct 28, 2004 #6
    Perhaps, i am missing something here, but what's all the fuss about???

    Just write : -x(2x^2+9x+60) = 0. So 0 is one solution. Then you have to solve 2x^2+9x+60 = 0. Since D = 81-2*4*60 < 0 You have no real solutions. can you incorporated compelx numbers ? If so, just continue as in the D > 0 case. if not, there are no solutions here...

  8. Oct 28, 2004 #7


    User Avatar

    good pont marlon, there is only one solution. it is x = 0. sorry i didnt even bother to check what D was.
  9. Oct 28, 2004 #8
    Most of us are not mindreaders, and don't know what people are really asking when they say "solve" and then post a function.
  10. Oct 28, 2004 #9

    Sorry, but do you know another way to solve a function ???

    i think not...

    marlon, the mind-reader
  11. Oct 28, 2004 #10
    I don't know of any way to "solve a function", just like I don't know how to "solve a banana".
  12. Oct 28, 2004 #11

    sweden, ja???

    are you into ABBA ???

  13. Oct 28, 2004 #12
    Nope. How many waffles have you eaten today...?
  14. Oct 28, 2004 #13

  15. Oct 29, 2004 #14


    User Avatar
    Gold Member


    solve that function
  16. Oct 30, 2004 #15

    hahaha, please ask a more difficult question...

    answer : x = 0

  17. Oct 30, 2004 #16
    Solving means finding the solutions guys...

    wow, what a revealing theory...

  18. Oct 30, 2004 #17


    User Avatar
    Gold Member

    That answer is only true if y is 0.
  19. Oct 30, 2004 #18
    yes indeed it is...

  20. Oct 30, 2004 #19
    if y were to be 5 the the question should be : solve x - 5. hence the answer is 5...

    beware that you do not violate the injectivity part of the definition of a function. With one x value, there can be at least one y-value, otherwise we do not have a function. Eg. x = 6 is NOT a function. y = x - 6 sure is...
    Ofcourse with one y-value there can be several x-values like in y = x²

  21. Oct 30, 2004 #20


    User Avatar
    Staff Emeritus
    Science Advisor

    "Solving means finding the solutions guys...

    wow, what a revealing theory...


    You still haven't understood what everyone is saying! Yes, "solve" means find the solutions- but to what problem?

    The orginal post just said "How do I solve this one? y= 3x<sup>3</sup> -9x<sup>2</sup>- 60x"

    That's not a "problem" that's just a statement. You then ASSUMED that the problem was "find all values of x that make y= 0" but that certainly is NOT the only possible problem that could be associated with a function.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Function ?
  1. Distance between points (Replies: 23)