Tangent to a 2D graph : tangent

### 3.5.5 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)``∈` `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)`