title: sympy: order of result from solving a quadratic equation
body: <p>I solved a quadratic equation using sympy:</p>
  
  <pre><code>import sympy as sp
  q,qm,k,c0,c,vt,vm = sp.symbols('q qm k c0 c vt vm')
  c = ( c0 * vt - q * vm) / vt
  eq1 = sp.Eq(qm * k * c / (1 + k * c) ,q)
  q_solve = sp.solve(eq1,q)
  </code></pre>
  
  <p>Based on some testing I figured out that only <code>q_solve[0]</code> makes physical sense. Will sympy always put <code>(b - sqrt(b**2 - 4*a*c))/2a</code> in the first place ? I guess, it might change with an upgrade ?</p>