Secant and Tangent Lines Applet

The applet shows secant lines converging to tangent lines. The applet draws a tangent line to a graph at a point marked by a draggable disk (which is red). By dragging this disk, you can move the point. A secant line is drawn from this point to another point, which is marked by another draggable disk (green). You can also set the x-coordinates of the point by entering them in the input boxes at the bottom of the applet. The slopes of the two lines are shown in the upper left corner.