IntroFoundations
Secant vs Tangent Line
Overview
Two kinds of lines on a curve. A secant cuts through at two points — measuring average change. A tangent touches at one point — measuring instantaneous change.
Key Concepts
1
Secant line: connects two distinct points on the curve → average rate of change
2
Tangent line: touches the curve at exactly one point → instantaneous rate
3
As the two secant points get closer, the secant → the tangent line
4
The slope of the tangent at x = a is the derivative f′(a)
See it in action
Use the interactive visualizer to explore this concept with real graphs.