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The parabola tool displays a movable parabola on the graph view. (See below:)

Parabola tool cursor:

The parabola tool also displays equations, coordinates and calculated values, and plots the curves, lines and points directly.

Select the parabola tool by clicking the button on the graph tools tool bar, or by selecting the 'Parabola' command from the 'Tools' menu.

A parabola is the path traced out by a point that moves so that it is always the same distance from a fixed line and a fixed point not on the line.

The line is called the 'directrix' of the parabola, and the point is called the 'focus' of the parabola. The parabola tool handles two types of parabolas. The 'y=' type, with horizontal directrix, and the 'x=' type, with vertical directrix. (See diagram below:)

When the parabola tool is selected, the parabola tool dialog box is displayed (See below:).

 Drag on the title bar at the top of the parabola tool dialog box to move it. Check the 'Focus' check box to display the focus of the parabola on the graph view. Check the 'Directrix' check box to display the directrix of the parabola on the graph view. Check the 'x=' check box for vertical parabolas. Leave unchecked for 'y=' parabolas. (See diagram above).
 Check the 'Trace' check box to trace the centre of the parabola along a function curve. Check the 'Snap to grid' option to locate the centre of the parabola at the corner of grid snap rectangles. Click the 'Cancel' button to stop using the parabola tool.

### Press the space bar on the keyboard to plot graphs of:

 the parabola. the focus of the parabola if the 'Focus' check box is checked. the directrix of the parabola if the 'Directrix' check box is checked.

## Changing the shape of the parabola:

With the parabola tool displaying the parabola on the graph view, click and hold the left mouse button while moving the mouse.

 Drag the mouse horizontally to change the width of the parabola. Drag the mouse vertically to change the height of the parabola. For fine adjustment, hold down a Shift key as well.
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