# Tangent lines

Here are two examples:

The green line is no tangent cause the line intersects the graph without just touching it. The read line is a tangent cause it just touches the graph in one point without intersecting it.

Mind the special case: A tangent line in an ininflection point does cross the graph of the function. Anyway, the red line is obviously the tangent in the point (0|0), having the same slope as the graph.

Also think about this: A line being tangent in one point may very well intersect the graph in some other point.

- Insert x into the function, so you got the point where the tangent touches
- Insert x into the derivation, so you got the slope m of the tangent.
- Insert m and the point into , then you got b