The vertex of quadratic function graph is commonly called extreme point. Ordinat of extreme point, namely
is called extreme value. whereas abscissa of extreme point, namely
is called extreme factor- making-extreme point.
2.1.7.3 Positive and Negative Definites
If a function has a positive value for each , so such function is called
positive definite function. Because its value is always positive, so If a
functionhas negative value for each , so such function is called negative definite
function so that Is a function is negative definite, then its whole graph is below
-axis. In order that the whole graph exists below
axis, so its should be and .
function will be i. positive definite
and ii. negative definite
and Figure 2.5 Position of parabola
2.1.7.4 Determining the Quadratic Functions Formula
2.1.7.4.1 Determining the Formula of Quadratic Function if its Turning Point is known
When the formula of quadratic function has been in the form of perfect square
then the coordinate of its vertex is . Thereby, if the vertex
is known, so the formula of its quadratic function is
2.1.7.4.2 Determining the Formula of Quadratic Function if the -intercept is
Know If the
-intercept of quadratic function with the curve equation is acquired if , so that the equation becomes:
with and
are the roots of quadratic equation Point
and are intersection point of quadratic function
with axis. Thereby, if the
-interccept at and
is known, so the formula of its quadratic function is:
where a is determinant if the other points passed by curve are known.
2.1.7.4.3 Determining the Fromula Quadratic Function if Three Point Passed by Parabola is Known.
The formula of quadratic function of parabola is also able to be determined if at least three points passed is known. Need three points because in
order to acquire the value of a, b, and c in the equation required at least three equations. At the previous descripstion, we can obtain the
formula of quadratic equation only with two points passed. This matter is brought on one of the points known is extreme point.
If it is known three points is passed by a parabola, so the formula of quadratic equation of the parabola can be determined by using elimination and
substitution method.
2.1.7.5 The Applications of Quadratic Function
