input: Write a python function to find the solutions of a quadratic equation.
  assert quadratic_equation(1, 5, 6) == (-3+0j, -2+0j)
  assert quadratic_equation(1, -3, 2) == (1+0j, 2+0j)
  assert quadratic_equation(1, 2, 1) == (-1+0j, -1+0j)
output: def quadratic_equation(a, b, c):
      import cmath
      d = cmath.sqrt(b**2 - 4*a*c)
      sol1 = (-b + d) / (2*a)
      sol2 = (-b - d) / (2*a)
      return (sol1, sol2)