In the Geogebra applet below, use the slider for Δx to change the gradient of the red secant line so that it approaches the gradient of the blue line which is tangent to the curve at point P. You can also change the location of point P by using the slider for x1 (the x-coordinate of P). The process by which the secant line becomes a better and better approximation of the tangent to the graph of a function at a...