In Exercises the curve y = ∫(x) has a vertical tangent at x = a if

In each case, the right- and left-hand limits are required to be the same: both + ∞ or both - ∞. Use graphs to investigate whether the curve has a vertical tangent at x = 0.

y = x^2/3

or if f(a+h)-f(a) h f(a+h)-f(a) h lim h0 lim h0