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

Can anyone solve this equation?

  1. Jan 24, 2005 #1
    Does anyone know how to solve the following equation:

    e^x-x^3+x^2-2x = 0.

    Thanks in advance.
  2. jcsd
  3. Jan 24, 2005 #2
    x = 1.727780...
    x = 4.098178...
  4. Jan 24, 2005 #3


    User Avatar
    Science Advisor
    Homework Helper

    It doesn't work that way...It's a transcendental equation.It's solutions are found only by approximation...Graphical method is the best to use...

  5. Jan 24, 2005 #4
    Do you know that without using LaTex you can still do superscripts using the [ sup ] [ /sup ] tags (without spaces)

    For example. e^x can be written as e[ sup ]x[ /sup ] (to produce) ex.

    Type in [ sup ] (without the spaces), copy it, then just paste it as you type. Then add the slash to the trailing tags.

    With just a little pasting your equation could look like this,...

    ex-x3+x2-2x = 0.

    Or even encapsulate the whole mess in a larger font size llike so,...

    ex-x3+x2-2x = 0

    The're even nestable. For example you could do something like the following without using latex at all.


    You can also do subscripts the same way using [ sub ] [ /sub ]

    Sorry. I just hate messy looking equations. :biggrin:
  6. Jan 24, 2005 #5


    User Avatar
    Science Advisor
    Homework Helper

    The good part is that,even written in this "horrible" way,it's still inteligible.Thankfully it didn't involve fractions... :tongue2:

  7. Jan 24, 2005 #6
    Yep, that's what I got too. These calculators never cease to amaze me. :approve:
  8. Jan 24, 2005 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    One way to come up with a solution for this type of problem is to simply to isolate an x on one side of the equation. Then make a guess, following guesses are made by simply recomputing using the most recent result.

    for example in this problem you can write

    [tex] x = \frac { e^x -x^3+x^2} 2 [/tex]

    With a starting guess of 1 the following sequence is generated

    Trouble is this particular formulation will not generate the second point. It is required that the slope of the function be less then 1 in the region of the solution.

    if you recast as

    [tex] x= ln (x^3 -x^2 +2) [/tex]

    You get a fixed point at the second solution but is much slower in converging.

    This process is know as a Fixed point solution. A web search may well provide more details.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook