input: Write a python function to find out the roots of a given quadratic equation.
  assert quadratic_roots(1, -7, 12) == (4.0, 3.0)
  assert quadratic_roots(1, -3, 2) == (2.0, 1.0)
  assert quadratic_roots(1, -2, 1) == 1.0
output: def quadratic_roots(a, b, c):
      import math
      discriminant = b**2 - 4*a*c
      if discriminant > 0:
          root1 = (-b + math.sqrt(discriminant)) / (2*a)
          root2 = (-b - math.sqrt(discriminant)) / (2*a)
          return (root1, root2)
      elif discriminant == 0:
          root = -b / (2*a)
          return root
      else:
          return None