Tangent to a 2D graph : LineTan

LineTan takes two arguments : an expression E_x of the variable x and a value x0 of x.
LineTan draws the tangent at x = x0 to the graph of y = E_x.
Input :

LineTan(ln(x),1)

Output :

the line y=x-1

Input :

equation(LineTan(ln(x),1))

Output :

y=(x-1)