(a) Find the slope of the tangent line for each function fat the given point.
(b) Find an equation of the tangent line to the graph of each function $f$ at the given point.
(c) Find the points, if any, where the graph of the function has a horizontal tangent line.
(d) Graph each function, the tangent line found in $(b),$ and any tangent lines found in $(\mathrm{c})$ on the same set of axes.
$$f(x)=\frac{x}{x+1}$ at (0,0)$