Chord → Tangent — Interactive

Type a function (use ^ for power). Hold Shift and drag the canvas to move x₀.
Symbolic (updates live)
\( \dfrac{f(x_0+h)-f(x_0-h)}{2h} \to f'(x_0) \)
Numeric

Graph — chord (secant) to tangent

Blue: f(x). Orange: tangent. Green: chord (secant). Central secant slope shown numerically near chord.