Given,
[tex]\lim_{x}^{a}\dfrac{x^{2/3}-a^{2/3}}{x-a}[/tex]
We can use L'Hopital's Rule to get,
[tex]\lim_{x}^{a}\dfrac{2}{3-\sqrt[3]{x}}[/tex]
Now plug in a,
[tex]\boxed{\dfrac{2}{3-\sqrt[3]{a}}}[/tex]
Hope this helps.
r3t40
