1. Graphing Quadratic Functions
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What happens with the vertex of a parabola when the parabola opens downward?
Counterexample:
We will provide a counterexample to show that the following statement is false.
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The vertex of a parabola is always the minimum of the graph. |
Let's recall that a graph of a quadratic function, y=ax^2+bx+c, opens upward whenever a is positive, and opens downward whenever a is negative.
In the case that a>0, the vertex of the parabola is its minimum. In the case that a<0, the vertex of the parabola is its maximum.
This tells us that any parabola that opens downward is a counterexample for the given statement.