To draw the line tangent to a curve at a particular point, from the home screen press to display the DRAW menu.
Press to place the Tangent function on the home screen.
Enter an expression in x or use the Y-VARS menu to select a previously stored function.
The syntax is: Tangent( expression, value ).
value represents the x-coordinate of the point on the curve where the tangent line is to be drawn.
Pressing will display the graph and draw the tangent line.
Use ClrDraw in the DRAW menu to redraw the graph without the tangent line.
Note: The Tangent command may also be used while viewing a function's graph. However, a particular point cannot be specified. The instructions are as follows.
Select Tangent in the DRAW menu, trace to the approximate point on the graph where the tangent line should be drawn, and press . The tangent line is drawn and the approximate value of the tangent line's slope, dy/dx, is displayed at the bottom of the screen.