input: Write a python function to find the roots of a quadratic equation.
  assert roots(1, -3, 2) == (2.0, 1.0)
  assert roots(1, -2, 1) == (1.0, 1.0)
  assert roots(1, 0, -4) == (2.0, -2.0)
output: def 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)
      else:
          return None