Every quadratic curve y = a x² + b x + c has a vertex point: the turning point where the curve stops heading down and starts going up.
Given the values a, b and c, you need to return the coordinates of the vertex. Return your answers rounded to 2 decimal places.
find_vertex(1, 0, 25) ➞ [0, 25]
# The vertex of y=x²+25 is at (0, 25).
find_vertex(-1, 0, 25) ➞ [0, 25]
# The vertex of y=-x²+25 is at (0, 25).
find_vertex(1, 10, 4) ➞ [-5, -21]
# The vertex of y=x²+10x+4 is at (-5, -21).
a will always be non-zero.