The line tangent to a curve at a particular point may be drawn while viewing a graph by first pressing to display TANLN, the tangent line function key.

Press .

If more than one curve is displayed, use the keys to select the desired curve and enter the x-coordinate of the point where the tangent line is to be drawn.

Press to draw the tangent line.

The slope, dy/dx, of the tangent line at the requested x-coordinate is displayed at the bottom of the screen. Use CLDRW in the DRAW menu to redraw the graph without the tangent line.

**Note:** The degree of accuracy of the displayed value for dy/dx will usually
depend on which derivative setting is selected in MODE. dxDer1 will typically
be more accurate than dxNDer. However, dxNDer is less restrictive and the
accuracy may be increased by choosing a smaller value for d in the tolerance
settings, accessed by pressing
.