In
order to find the vertex of a quadratic function, a graph must already be displayed
on the screen. To learn how to enter and graph a function, go to **Graphing
a Function**. Consider the quadratic function, ,
which is graphed below in a standard window:

For
this function, the vertex is the **minimum
point**. To find the vertex, press **2nd TRACE [CALC], **then select
**3:Minimum** by pressing **3.**

The above last screen is
asking for a left bound. Use the **Left Arrow Key** to move the flashing cursor
slightly to the left of the minimum point and then press **ENTER.** The left
bound is now marked, as shown below, with a small arrow towards the top of the
screen.

The above last
screen is asking for a right bound. Now use the **Right** **Arrow Key **
to move the flashing cursor slightly to the right of the minimum point and then
press **ENTER.**

Note that both the left bound and right bound are marked with a small arrows towards the top of the screen as is seen above. That screen asks for a guess.

Move
the curser as close to the minimum point as possible, and press **ENTER** again.
The last screen shows that the vertex is about **(0.5,
- 6.25)**.

To find the vertex of a
parabola that opens downward instead of upward, repeat the above process, except
select **4:Maximum** instead of **3:Minimum**.

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