title: python nsolve/solve triple of equations
body: <p>I keep getting errors when I tried to solve a system of three equations using the following code in python3:</p>
  
  <hr>
  
  <pre><code>import sympy
  from sympy import Symbol, solve, nsolve
  
  x = Symbol('x')
  y = Symbol('y')
  z = Symbol('z')
  
  eq1 = x - y + 3
  eq2 = x + y
  eq3 = z - y
  
  print(nsolve( (eq1, eq2, eq3), (x,y,z), (-50,50)))
  </code></pre>
  
  <hr>
  
  <p>Here is the error message:</p>
  
  <blockquote>
    <p>Traceback (most recent call last):
      File
    "/usr/lib/python3/dist-packages/mpmath/calculus/optimization.py", line
    928, in findroot
       fx = f(*x0)
    TypeError: () missing 1 required positional argument:
    '_Dummy_15'</p>
  </blockquote>
  
  <p>During handling of the above exception, another exception occurred:</p>
  
  <blockquote>
    <p>Traceback (most recent call last):   File "", line 1, in
       File "", line 12, in    File
    "/usr/lib/python3/dist-packages/sympy/solvers/solvers.py", line 2498,
    in nsolve
       x = findroot(f, x0, J=J, **kwargs)
      File
    "/usr/lib/python3/dist-packages/mpmath/calculus/optimization.py", line
    931, in findroot
       fx = f(x0[0])
    TypeError: () missing 2 required positional arguments:
    '_Dummy_14' and '_Dummy_15'</p>
  </blockquote>
  
  <hr>
  
  <p>The strange thing is, the error message goes away if I only solve the first two equation --- by changing the last line of the code to</p>
  
  <pre><code>print(nsolve( (eq1, eq2), (x,y), (-50,50)))
  </code></pre>
  
  <p>output:</p>
  
  <pre><code>exec(open('bug444.py').read())
  [-1.5]
  [ 1.5]
  </code></pre>
  
  <p>I'm baffled; your help is most appreciated!</p>
  
  <p>A few pieces of additional info:</p>
  
  <ul>
  <li><p>I'm using python3.4.0 + sympy 0.7.6-3 on ubuntu 14.04.  I got the same error in python2</p></li>
  <li><p>I could solve this system using </p>
  
  <p>solve( [eq1,eq2,eq3], [x,y,z] )</p></li>
  </ul>
  
  <p>but this system is just a toy example; in the actual applications the system is non-linear and I need higher precision, and I don't see how to adjust the precision for solve, whereas for nsolve I could use <code>nsolve(... , prec=100)</code></p>
  
  <p>THANKS!</p>