------
## 最终结论
```python
def parabola_focus(a, b, c):
    D = b**2 - 4*a*c
    focus_x = -b / (2 * a)
    focus_y = (1 - D) / (4 * a)
    return (focus_x, focus_y)

# Test cases
assert parabola_focus(5,3,2) == (-0.3, 1.6)
assert parabola_focus(9,8,4) == (-0.4444444444444444, 2.25)
assert parabola_focus(2,4,6) == (-1.0, 4.125)
```