The blue curve is the graph of [math]y=f(x)[/math]. Move the slider to change the position of point [math]P[/math] on the curve. Click the checkboxes to show the tangent line to the curve at [math]P[/math] (it also displays the gradient of the line) and the point whose [math]y-[/math]coordinates that represent the gradient of the [math]P[/math] (that is, to plot the graph of [math]y=f'(x)[/math])