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The line tool displays a line segment cursor or a vector cursor on the graph view:

 Cursor for line mode: Cursor for vector mode:

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

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

Checking the 'vector' check box changes the line tool into 'vector mode'. When the 'vector' check box is not checked, the line tool is in 'line mode'.

## Line mode:

With the 'vector' check box not checked the line tool is in 'line mode' and this dialog box displays the equation of the line and other helpful information. In the screen shot below, the line segment has been captured by the parabola function as its tangent. By moving the mouse left and right, the tangent line travels around the curve.

 Drag on the title bar at the top of the line tool dialog box to move it. Check the 'Trace' check box to trace the line along a function curve as an approximate tangent to the curve. Check the 'Snap to grid' option to locate the centre of the line at the corner of grid snap rectangles. Click the 'Cancel' button to stop using the line tool.

The line tool dialog box displays:

 The equation of the line through the segment: y = mx + c The coordinates of the centre of the line segment. The length of the line segment. The angle the segment makes with the positive 'x' axis direction.

Press the space bar on the keyboard to plot the equation for the line.

## Changing the length and gradient of the line segment:

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

 Drag the mouse horizontally to change the gradient of the line segment. Hold down a 'Ctrl' key on the keyboard while you drag the mouse horizontally to change the length of the line segment. For fine adjustment, hold down a Shift key as well.

## Vector mode:

With the 'vector' check box checked the line tool is in 'vector mode' and this dialog box displays the 'i' and 'j' components of the vector, the length and direction of the vector, as well as the coordinates of the tail of the vector.

The vector tool dialog box displays:

 The i and j components of the vector. The coordinates of the tail of the vector. The length of the vector. The angle the vector makes with the positive 'x' axis direction.
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