------
## 最终结论
```python
def parabola_vertex(a, b, c):
    x = -b / (2 * a)
    y = (4 * a * c - b ** 2) / (4 * a)
    return (x, y)

# Test cases
assert parabola_vertex(5, 3, 2) == (-0.3, 1.55)
assert parabola_vertex(9, 8, 4) == (-0.4444444444444444, 2.2222222222222223)
assert parabola_vertex(2, 4, 6) == (-1.0, 4.0)
```