The document discusses the concept of differentiability using limits and four examples: 1) The function f(x) = x - 5 is not differentiable at x = 5 since the left and right hand derivatives are not equal. 2) The function f(x) = x^x, 0 ≤ x < 2 and f(x) = (x-1)x, 2 ≤ x < 3 is not differentiable at x = 2 since the left and right hand derivatives are not equal. 3) The function f(x) = x^2, x ≤ 1 and f(x) = 1/x, x > 1 is not differentiable at x = 1 since the left and