input: Write a python function to solve a quadratic equation given coefficients a, b, and c.
  assert solve_quadratic(4, 1, -3) == (0.75, -1.0)
  assert solve_quadratic(1, -3, 2) == (2.0, 1.0)
  assert solve_quadratic(1, 2, 1) == (-1.0, -1.0)
  assert solve_quadratic(1, 0, -4) == (2.0, -2.0)
output: def solve_quadratic(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