The dy/dx command finds a numeric derivative, which approximates the first derivative of an expression with respect to the x variable at a chosen value for x or at the trace cursor location while viewing a graph.
While viewing the graph of a function, press to view the CALCULATE menu.
If more than one function is graphed, use to select the desired curve. Enter the x-coordinate of the point on the curve for which the value of the derivative is needed (or trace the curve to the approximate point) and press . The value (or approximate value) of dy/dx at the point is displayed at the bottom of the screen.
Note: The value of the derivative is found by computing the slope of the line through the points and where .