Texas Instruments TI-83 PLUS - Manual (Page 226)

TI-83 Plus Draw Instructions 223
Tip: Change the fixed decimal setting on the mode screen if you want to see
fewer digits displayed for
X and the equation for Y .
Drawing a Tangent Line from the Home Screen or a Program
Tangent( (tangent line) draws a line tangent to expression in terms of X ,
such as Y 1
or X
2 , at point X = value . X can be an expression. expression is
interpreted as being in Func mode.
Tangent( expression , value )