Numeric Derivative via Secant Lines

① This example demonstrates how the slope of a secant line approaches the tangent slope as the step size decreases, visually illustrating the concept of a numerical derivative. ② The core mathematical concept is the limit definition of the derivative, involving functions, tangents, secants, slopes, and numerical approximation. ③ Construction highlights: using GeoGebra's Textfield and InputBox commands to dynamically adjust step parameters epsilon and delta, constructing the secant segment (SecSeg) with Segment and Line commands, computing horizontal/vertical increments (delx, dely) and slope (m), and displaying related text objects (delyText, delxText, slopeText) along with an auxiliary function g. ④ Suitable for high school and introductory college calculus students, this interactive tool helps learners grasp the intuitive meaning of the derivative limit, and serves as an effective classroom demonstration for linking numerical approximation with graphical visualization.