Comment #160 on issue 1694 by smichr: solve has many issues with fractions
http://code.google.com/p/sympy/issues/detail?id=1694

The branch is 1694.

Thanks for the problem, Aaron. This flushed up some more errors. Now, all four solution sets have the same first solution that is equivalent to what you recalled:

eq = f - (2*x + 2*y + sqrt(x**2 + y**2))
a = x*y

Solving eq for x
x1, x2 = solve(eq, x)
solve(a.subs(x, x1).diff(y), y)
[2*f/7 - f*2**(1/2)/14, f/3 - I*f*2**(1/2)/6, f/3 + I*f*2**(1/2)/6]
solve(a.subs(x, x2).diff(y), y)
[2*f/7 - f*2**(1/2)/14, 2*f/7 + f*2**(1/2)/14, f/3 - I*f*2**(1/2)/6, f/3 + I*f*2**(1/2)/6]

Now in terms of y
y1, y2 = solve(eq, y)
solve(a.subs(y, y1).diff(x), x)
[2*f/7 - f*2**(1/2)/14, f/3 - I*f*2**(1/2)/6, f/3 + I*f*2**(1/2)/6]
solve(a.subs(y, y2).diff(x), x)
[2*f/7 - f*2**(1/2)/14, 2*f/7 + f*2**(1/2)/14, f/3 - I*f*2**(1/2)/6, f/3 + I*f*2**(1/2)/6]

As this shows there are potentially more errors lurking we can either try close off this issue and start a new issue for additional solving enhancement (namely, tsolve and solvable non-linear systems) or try to put this in all together. The only thing I would like to add at this point is the enhanced Lambert solver, but that can wait.

Does anyone have a preference?

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