Tangent Line as Limiting Position of Secant Lines

This applet shows that tangent line at a point P is obtained as limiting position of secant lines through the point P. Use slider a to select point of contact P. Use button on bottom left of the geometric view to start and pause the animation.
Discuss why value of derivative at a point equals slope of tangent line. For more on interpretation of derivative check my online book "Flipped Classroom Calculus of Single Variable" https://versal.com/learn/vh45au/