def optfun(x0, k1=3, k2=20):
  # задаем вычисление оптимизируемой функции
  f=x0**4 + k1*x0**3 - k2*x0**2 + x0 - 1

  return f

def dihotomia(x0, a, b, epsg=0.05):
  xlist = [x0]
  iter = 0
  while abs(b-a) > epsg:
    x = (a + b) / 2.0
    fx = optfun(x)
    fa = optfun(a)
    xlist.append(x)
    if (fx < 0 and fa < 0) or (fx > 0 and fa > 0):
      a = x
    else:
      b = x
  return xlist

x0 = 4
print(dihotomia(x0, a = -6, b = 0))