input: Write a python function to find the roots of a quadratic equation.
  assert quadratic_roots(2, 5, -3)==(-3.0, 0.5)
  assert quadratic_roots(1, -7, 12)==(4.0, 3.0)
  assert quadratic_roots(1, -3, 2)==(2.0, 1.0)
output: def quadratic_roots(a, b, c):
      import cmath
      d = b**2 - 4*a*c
      root1 = (-b + cmath.sqrt(d)) / (2*a)
      root2 = (-b - cmath.sqrt(d)) / (2*a)
      return (root1.real, root2.real) if d >= 0 else (root1, root2)