Use this applet to explore how the definition of the derivative relates to the secant and tangent lines at a point (a, f(a)).[br][br]The red slider controls the location of the point (a,f(a)).[br]The blue slider controls the value of "h" that determines the separation of the two points used for the secant line.[br][br]Watch what happens to the secant line as you decrease the value of h. [br]Pay specific attention to the slope in the equation of the secant line shown at the bottom.[br]What happens to the secant line when h = 0? Why?[br][br]Now turn on the tangent line to see how it compares to the secant line.