Explain why the function is differentiable at the given point then find the linearization of x/(x+y)

The differentiable functions are one for which there is a departure line at each position on the graph. The digression line to the graph y = f (x) at the point (a, f (a)) is given by the equation. Moreover the other line (at least near (a, f (a))), the function La is the best linear and find the best linear guess to the function f (x) = sqrt (x) near 100.