A parabola that opens downwards has a maximum at its vertex. One way to find it is to take the derivative of the parabola's equation (for y = x2, for example, this is y = 2x), set that to zero, and solve (2x = 0; x = 0). This works because the only horizontal tangent line of a parabola is at its vertex.
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It is either a maximum or minimum value depending on its downwards shape or its upwards shape
"Any light beam moving vertically downwards in the concavity of the parabola (parallel to the axis of symmetry) will bounce off the parabola moving directly towards the focus." http://en.wikipedia.org/wiki/Parabola
Change it from positive to negative
Vertex
The vertex is either the minimum (very bottom) or maximum (very top) of a parabola.
When you look at the parabola if it opens downwards then the parabola has a maximum value (because it is the highest point on the graph) if it opens upward then the parabola has a minimum value (because it's the lowest possible point on the graph)
It is either a maximum or minimum value depending on its downwards shape or its upwards shape
Downwards
A parabola's maximum or minimum is its vertex.
A parabola opening up has a minimum, while a parabola opening down has a maximum.
If the value of the variable is negative then the parabola opens downwards and when the value of variable is positive the parabola opens upward.
The point on the parabola where the maximum area occurs is at the vertex of the parabola. This is because the vertex represents the maximum or minimum point of a parabolic function.
"Any light beam moving vertically downwards in the concavity of the parabola (parallel to the axis of symmetry) will bounce off the parabola moving directly towards the focus." http://en.wikipedia.org/wiki/Parabola
Change it from positive to negative
The extreme point it the highest or lowest point of the parabola (depending if it is concave downwards or upwards). It is the point of the parabola tat is closest to the focus. the extreme point lies on the axis of symmetry.
Vertex
The vertex is either the minimum (very bottom) or maximum (very top) of a parabola.