title: Evaluation of Sympy expression doesn't yield correct result
body: <p>Why is the difference between <code>fdeno</code> and <code>deno2</code> so big in the following code?</p>
  <pre class="lang-py prettyprint-override"><code>from sympy import symbols
  
  sign2 = symbols('sign2')
  
  deno = sign2*(sign2 - 1.6)*(sign2 - 1.5)*(sign2 - 1.4)*(sign2 - 1.3)*(sign2 - 1.2)*(sign2 - 1.1)*(sign2 - 1.0)*(sign2 - 0.9)*(sign2 - 0.8)*(sign2 - 0.7)*(sign2 - 0.6)*(sign2 - 0.5)*(sign2 - 0.4)*(sign2 - 0.3)*(sign2 - 0.2) 
  
  &quot;&quot;&quot;not include the term (sign2 -0.1)&quot;&quot;&quot;
  
  fdeno = float(deno.evalf(subs={sign2:round(0.1,1)},n=15))
  
  deno2 = 0.1*(0.1-1.6)*(0.1-1.5)*(0.1-1.4)*(0.1 - 1.3)*(0.1 - 1.2)*(0.1 - 1.1)*(0.1 - 1.0)*(0.1 - 0.9)*(0.1 - 0.8)*(0.1 - 0.7)*(0.1 - 0.6)*(0.1 - 0.5)*(0.1 - 0.4)*(0.1 - 0.3)*(0.1 - 0.2) 
  
  print(fdeno,&quot;//&quot;,deno2)
  
  # Output:
  0.0 // -0.00013076743679999998
  </code></pre>