The square root function f(x) = x. (Because this function is only denned for x 0, you can only use x > 0.) The

The square root function f(x) = √x. (Because this function is only denned for x ≥ 0, you can only use Δx > 0.)
The following functions all fail to be differentiable at x = 0. In each case, graph the function, see what happens if you try to compute the derivative as the limit of the slopes of secant lines, and say something about the tangent line.