Definition:Tangent to Curve

Definition
Let $f: \R \to \R$ be a real function.

Let the graph of $f$ be depicted on a Cartesian plane.


 * TangentToCurve.png

A tangent to $f$ is a straight line which intersects the graph of $f$ locally at a single point.

In the above diagram, the tangent is the straight line passing through $A$.