code: def sum(self):
          
          ak = self.coefficients()
          ak2 = ak[::2]
          n = len(ak2)
          Tints = 2/(1-(2*np.arange(n))**2)
          val = np.sum((Tints*ak2.T).T, axis=0)
          a_, b_ = self.domain()
          return 0.5*(b_-a_)*val
docs: Evaluate the integral over the given interval using
          Clenshaw-Curtis quadrature.