From GeoGebra Manual
- Tangents to a conic section can be produced in several ways (also see command Tangent):
- Selecting a point A and a conic c produces all tangents through A to c.
- Selecting a line g and a conic c produces all tangents to c that are parallel to line g.
- Selecting a point A and a function f produces the tangent line to f in x = x(A).
- Note: x(A) represents the x-coordinate of point A. If point A lies on the function graph, the tangent runs through point A.