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.
More formally, differential calculus defines the instantaneous rate of change (the derivative) of a mathematical function's value, with respect to changes of the variable. The derivative is defined as a limit of a difference quotient.