f is continuous at c if and only if for every ε>0 there exists δ>0 such that |x−c|<δ ⇒ |f(x)−f(c)|<ε.
｢f(x) Ƚx￫c｣ = f(c)
┄
ᐥA function f:A￫ℝ is differentiable at c if and only if
｢(f(x)−f(c))/(x−c) Ƚx￫c｣
exists.
The value of the limit, called the derivative of f at c, is denoted by f(x)ᐁx｢c｣.ᐥ
