Texas Instruments TI-83 PLUS - Manual (Page 225)

TI-83 Plus Draw Instructions 222
Drawing Tangent Lines
Drawing a Tangent Line Directly on a Graph
To draw a tangent line when a graph is displayed, follow these steps.
1. Select 5:Tangent( from the
DRAW
menu.
2. Press † and } to move the cursor to the function for which you want
to draw the tangent line. The current graph’s Y= function is displayed
in the top-left corner, if ExprOn is selected.
3. Press ~ and | or enter a number to select the point on the function at
which you want to draw the tangent line.
4. Press Í . In Func mode, the X value at which the tangent line was
drawn is displayed on the bottom of the screen, along with the
equation of the tangent line. In all other modes, the
dy/dx value is
displayed.