The following are true of a vertex (algebraic):

• The vertex can be a minimum or maximum point.


• For parabolas opening up or down, the x-value of the vertex is equidistant from the x values of the x-intercepts.


• For parabolas opening up or down, the y-value of the vertex is equidistant from the y value of the focus and the closest point on the directrix.


• For parabolas opening up or down, the x-value of the vertex is same as the x-value of all the points on the axis of symmetry.


• The x-value can be found using the formula h = 
  -b2a
  for a parabola with the equation y = ax² + bx + c.


• The y-value can be found by using the x-value into the equation, y = ax² + bx + c, and simplifying.


• Similar statements can be made for parabolas opening to the left and right.