title: numerical value for an expression in sympy
body: <p>sympy is giving me the following expression:</p>
  
  <pre><code>2.8*x**2 - 4.0*x*Integral(1.0*x**2*sqrt(-x**2 + 1), (x, -1.0, 0.0)) + 1.33333333333333*x + 0.133333333333333
  </code></pre>
  
  <p>i want sympy to give me numerical values for the coefficients. how can i do this? .evalf and N() didn't work.</p>
  
  <p>this is my code</p>
  
  <pre><code>from numpy import *
  from sympy import *
  from matplotlib.pyplot import *
  
  x = Symbol ('x')
  
  #The function we are required to approximate
  f1 = -1.0*x
  f2 = 1.0*x
  
  
  phi_0=1.0
  phi_1 = 2.0*x
  phi_2 = 4.0*x*x-1
  
  w = 1.0*sqrt(1.0-x*x)
  
  #compute the coefficient
  
  c_0 = integrate(f1*phi_0*w, (x, -1.0, 0.0))+integrate(f2*phi_0, (x, 0.0, 1.0)) 
  c_1 = integrate(f1*phi_1*w, (x, -1.0, 0.0))+integrate(f2*phi_1, (x, 0.0, 1.0)) 
  c_2 = integrate(f1*phi_2*w, (x, -1.0, 0.0))+integrate(f2*phi_2, (x, 0.0, 1.0)) 
  
  fapprox2 = c_0*phi_0+c_1*phi_1+c_2 *phi_2
  </code></pre>