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 to place TanLn on the home screen.
Enter the expression in x (such as y1 or sin(x)) or press to select the function from the list of previously stored functions.
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.