The y-coordinate of the vertex of a parabola in ##y=ax^2 + bx + c## is ##k = (4ac – b^2)/(4a)##

explanation: The vertex of a parabola, written in ##y= ax^2 + bx + c## , denoted by the ordered pair ( h, k ) in which h is the x-coordinate and k is the y-coordinate is obtained using the formulas below:

##h = -(b)/(2a)##

##k = (4ac – b^2)/(4a)##