Kelly's story is truly inspirational. Kelly has shown that pure determination, dedication and hard work can and does change a person's life. At Life Leisure we have loved being part of Kelly's journey.
In calculus (a branch of mathematics), a differentiable function of one real variable is a function whose derivative exists at each point in its domain.
1 The function f (x) = x 2 + 2 x + 3 is differentiable everywhere, with the derivative f â²(x) = 2 x + 2. 2  This function has a unique critical point â1, because it is the unique number x 0 for which 2 x 0 + 2 = 0. 3  This point is a global minimum of f.