The equation of a parabola has been graphed and the equation displayed using
concatenate. The rate of change has been determined and graphed. To this
graph a trendline is added. The trendline equation is displayed. Then the
parabola is modified and the graph representing the rate of change adjusts.
Unfortunately, the equation of the trendline doesn't change. How can the
display equation of the trendline be displayed dynamicly?