Tangent to a 2D graph : tangent

See also : for plane geometry and for 3D geometry.
tangent takes two arguments : an geometric object and a point A.
tangent draws tangent(s) to this geometric object crossing through A. If the geometric object is the graph G of a 2D function, the second argument is either, a real number x0, or a point A on G. In that case tangent draws a tangent to this graph G crossing through the point A or through the point of abscissa x0.
For example, define the function g

g(x):=x^2

then the graph G={(x,y) $\in$ $\mathbb {R}$², y=g(x)} of g and a point A on the graph G:

G:=plotfunc(g(x),x);
A:=point(1.2,g(1.2));

If we want to draw the tangent at the point A to the graph G, we will input:

T:=tangent(G, A)

or :

T:=tangent(G, 1.2)

For the equation of the tangent line, input :

equation(T)