Quote:

I have never used Maclaurin series before. Therefore, I don't really understand the term $\displaystyle o(x^{2/3})$, so if you can explain me, then that would be great.

I suppose it would not help telling that Maclaurin series is Taylor series at x = 0. Quote:

Also I did use L'Hopital Rule for solving 1st question and I check limit left-hand = right-hand to prove it's not differentiable. However, when I apply the L'Hopital Rule, I get a constant as the limit, not infinity. Therefore, I'm not sure if I'm applying it in the right situation or not.

Using