Question: 
Write a function to find the directrix of a parabola.


Model's Code:
def parabola_directrix(a, b, c):
    return -((b**2 - 4*a*c) / (4*a))



Sample Correct Code:
def parabola_directrix(a, b, c): 
  directrix=((int)(c - ((b * b) + 1) * 4 * a ))
  return directrix


Asserts:
assert parabola_directrix(5,3,2)==-198
assert parabola_directrix(9,8,4)==-2336
assert parabola_directrix(2,4,6)==-130


Tests:
Test 1 of 3: FAIL: AssertionError()

Test 430 of 974: 314/430 (73.0232558139535%): failed