www.varsitytutors.com/hotmath/hotmath_help/topics/vertex-of-a-parabola

y=ax2+bx+c . But the equation for a parabola can also be written in "vertex form": y=a(x−h)2+k. In this equation, the vertex of the parabola is the point (h,k) .

www.purplemath.com/modules/grphquad2.htm

... a quadratic's leading coefficient as it relates to the graph, and discusses the vertex and how to find it. ... Also, if a is negative, then the parabola is upside- down.

www.mathwarehouse.com/geometry/parabola/vertex-of-a-parabola.php

Finding Vertex from Standard Form. The x-coordinate of the vertex can be found by the formula −b2a, and to get the y value of the vertex, just substitute −b2a, ...

www.khanacademy.org/math/algebra/quadratics/quad-standard-form-alg1/v/ex3-completing-the-square

Sal rewrites the equation y=-3x^2+24x-27 in vertex form (by completing the square) in order to identify the vertex of the corresponding parabola.

www.virtualnerd.com/algebra-1/quadratic-equations-functions/graphing/graph-basics/vertex-example

The vertex of a quadratic equation is the minimum or maximum point of the ... problem; skill; vertex; parabola; quadratic function; maximum; minimum; max; min ...

algebralab.org/lessons/lesson.aspx?file=Algebra_quad_vertex.xml

The vertex of a parabola is the high point or low point of the graph. The method you use to find the vertex will depend on the form in which the function is given.