To use this applet: click and drag points Q and P back and forth on the curve. You can also select points P and Q by
clicking on their labels and use key 'Arrow left' to move selected point to the left and 'Arrow right' to move selected point to the right
along the curve.
Observe how the secant line through the points P and Q changes as you move the points along the curve.
Consider how the green secant line becomes better and better approximations of the orange tangent line, as you move the point Q closer
and closer to the point P.
Notice that if P and Q are at the same point, there is no secant line, since it takes two points to determine the secant line. That is,
the secant line disappears, although you will still see the orange tangent line.
You can change the position and scale of the graph. Select the graph by clicking on it and then use controls keys from
table below or use buttons on the graph.
Also you can moving between graph, points and buttons by 'Tab' button.