The SecantTangent applet shows a secant line converging on a tangent line. The applet draws a tangent line to a graph at a point marked by a draggable disk (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 at the upper left, but you can turn off the display of the tangent slope if, for example, you want the user to estimate the slope of the tangent line from the slopes of secant lines.
