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Re: Equation problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109162] Re: Equation problem
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Wed, 14 Apr 2010 23:12:30 -0400 (EDT)
  • References: <hq39ug$na6$1@smc.vnet.net>

What you want is mathematically impossible. x and y are not linearly
related. Anyway, to bring you as close as possible to what you want
you could try to use the correct Mathematica syntax for your equation:

y == ((1 + Sqrt[5.71 10^8/x])*x)/6.3810^9

double = to make it a real equation, otherwise it's a Set operation.
Square brackets for functions and a capital letter for any built-in
function. Powers of 10 written as powers of 10 and not of e. Then you
can use Solve to solve this equation for x:

Solve[y == ((1 + Sqrt[5.71 10^8/x])*x)/6.3810^9, x]

 {{x ->
   2.27747*10^-28 (1.25358*10^36 + 7.70097*10^34 y -
      4.39404*10^35 Sqrt[8.13912 + 1. y])}, {x ->
   2.27747*10^-28 (1.25358*10^36 + 7.70097*10^34 y +
      4.39404*10^35 Sqrt[8.13912 + 1. y])}}

So, two solutions none of which have the shape you'd like. But as said
above that can't be done, not in Mathematica not in anything else.

Cheers -- Sjoerd



On Apr 14, 4:40 am, Asttro <imor... at gmail.com> wrote:
> I just started using Mathematica and have no idea how to do the following=
...
>
> I have the starting equation:
>
> y=((1+sqrt(5.71e8/x))*x)/6.38e9
>
> What I want is to obtain x=a+b*y, where a and b are parameters.
>
> Is this possible in Mathematica?



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