Checkpoint — limits

You now hold every idea calculus is built on: a function is a single-valued rule; slope is rise over run; a limit is the value f(x) approaches; continuity is limit = value; and the derivative is the tangent slope born from a shrinking secant.

Next stop: World 2 — the Derivative Lab, where you turn this single limit into a toolbox of rules and watch tangent planes glide across 3D surfaces.