50g

Hello, all. I am an AP Calculus teacher with many years experience 
using the 48G. Now trying to make the transition to the 50G and some 
things don't work the same way.

For instance, on the 48, you can define N(x)= x-F(x)/F'(x), define F
(x), say x^3-7, enter a numeric value, press N on the var list, and 
after eval, have a second iteration of the approximate root of F(x) 
near x. So, the N(x) recognizes x, F(x) and F'(x).

When the same strategy is used on the 50, I always get an answer of 
infinity. Either the N function doesn't recognize the F or the 
derivative is made equal to zero. Any ideas?

Secondly, I have tried many different ways to graph f(x)=x^(odd 
fractional power), for instance x^(5/3). It seems crazy, but the only 
way I can get the 50 to give the entire graph is to let F(x) = x^2/ x
(1/3). This is truly pathetic and I hope someone knows a more elegant 
solution. Thanks in advance for all help!