title: "Can't convert expression to float" error with sympy
body: <p>I am trying to solve the equations  like this,</p>
  
  <pre><code>from sympy.solvers import solve
  from sympy import Symbol
  import math
  
  x = Symbol('x')
  
  A, B = 1, 2
  
  print(solve((x) + (A/math.sqrt(x**4)) - (B * math.exp(-x)), x))
  
  
  Traceback (most recent call last):
    File "C:\Users\****\Desktop\Python Stuff\****\***.py", line 7, in &lt;module&gt;
      print(solve((x) + (A/math.sqrt(x**4)) - (B * math.exp(-x)), x))
    File "C:\Users\****\AppData\Local\Programs\Python\Python37\lib\site-packages\sympy\core\expr.py", line 280, in __float__
      raise TypeError("can't convert expression to float")
  TypeError: can't convert expression to float
  </code></pre>
  
  <p>Why this is happening?</p>