Results 1 to 7 of 7

Math Help - This is not rocket science but I am stuck!

  1. #1
    Banned
    Joined
    Jun 2009
    Posts
    3

    This is not rocket science but I am stuck!

    Hi,

    Well this is the formula:

    x(y+500)/(x+y+500) = 1520

    x should be near 2249 and y, near 4189.

    Could you help me to solve that equation, step by step. My knowledge of algebra is very low and quite far away. ....45 years away!

    Thanks!

    Alain
    Last edited by Jameson; June 16th 2009 at 11:26 AM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    Quote Originally Posted by AlainB View Post
    Hi,

    Well this is the formula:

    x(y+500)/(x+y+500) = 1520

    x should be near 2249 and y, near 4189.

    Could you help me to solve that equation, step by step. My knowledge of algebra is very low and quite far away. ....45 years away!

    Thanks!

    Alain
    Hi Alain, is your equation \frac{x(y+500)}{(x+y+500)} = 1520?

    I'm not exactly sure what it is your trying to do, could you explain further?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,545
    Thanks
    1394
    You cannot solve an equation in two variables for specific values of both variables.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    Just to add to HallsofIvy's post, if you have n number of variables, you need n number of equations.

    With yours above you can get y in terms of x, is that what you need?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Banned
    Joined
    Jun 2009
    Posts
    3
    Hi,

    Thanks! You see, I would like to use excell to compute the values of 2 resistors in parallel combine with a variable resistor to obtain a certain output resistance value. Like in the image the output value (R eqv.) would be between 1520 and 1660 Ohms when the variable resistor is turned from 0 to 100%. The values computed for the 2 resistors are 2249 and 4189.

    This is the reply that I received from another forum about that:

    It's fairly straightforward, if the resistances are x and y then

    x(y+500)/(x+y+500) = 1520
    y(x+500)/(x+y+500) = 1660

    I was lazy and solved them iteratively in Excel, if you did it manually - you'd get a quadratic, the solutions are:

    x=(377000√17+1861000)/(325√17+179)
    y=(1625√17+5875)/3





    Now if possible I would like to have the step by step sequence for solving that problem. I would then be able to do an Excell sheet to compute different scenario.

    Thanks again!

    Alain
    Last edited by Jameson; June 16th 2009 at 11:28 AM.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Banned
    Joined
    Jun 2009
    Posts
    3
    Hi,

    Thanks! You see, I would like to use excell to compute the values of 2 resistors in parallel combine with a variable resistor to obtain a certain output resistance value. Like in the image the output value (R eqv.) would be between 1520 and 1660 Ohms when the variable resistor is turned from 0 to 100%. The values computed for the 2 resistors are 2249 and 4189.

    This is the reply that I received from another forum about that:

    It's fairly straightforward, if the resistances are x and y then

    x(y+500)/(x+y+500) = 1520
    y(x+500)/(x+y+500) = 1660

    I was lazy and solved them iteratively in Excel, if you did it manually - you'd get a quadratic, the solutions are:

    x=(377000√17+1861000)/(325√17+179)
    y=(1625√17+5875)/3





    Now if possible I would like to have the step by step sequence for solving that problem. I would then be able to do an Excell sheet to compute different scenario.

    Thanks again!

    Alain
    Last edited by Jameson; June 16th 2009 at 11:29 AM.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by AlainB View Post
    Well, let's keep it simple!

    The previous post explain wy I need the equation solved. But we can forget about electronic.

    Is it possibe to solve x and y with those 2 equations? Mr F says: Yes. Using a TI-89 I got x = 2248 and y = 4192 (rounded to the nearesr whole number).

    x(y+500)/(x+y+500) = 1520
    y(x+500)/(x+y+500) = 1660

    As previously said the values should be near 2249 and 4189.

    Ultimately I would like to have an Excel sheet that will compute different scenarios as needed:

    Inputs:
    VR...............................500
    From R eqv low.............1520
    To R eqv high...............1620

    Results:
    R1..............................2249
    R2..............................4189

    The Excel part I could probably do by myself if I can just get the final algebra equations.

    Thanks!

    Alain
    ..
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Rocket problem
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 23rd 2010, 10:05 PM
  2. Rocket in the Air
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: April 6th 2010, 03:55 AM
  3. A Rocket in the Air
    Posted in the Pre-Calculus Forum
    Replies: 5
    Last Post: December 8th 2009, 01:59 AM
  4. A model rocket...
    Posted in the Calculus Forum
    Replies: 1
    Last Post: November 12th 2009, 02:02 PM
  5. Rocket Launched
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: September 25th 2008, 01:40 PM

Search Tags


/mathhelpforum @mathhelpforum