50g

> 1/(square root of x^2-16)

Works fine here.  

Here is a little cut out from this quite nice discussion from a few
years back.

'1/(x^4-1)'
TI89: 0.278 s.
HP49G+: 1.100 s.

'1/(x^4+1)'
TI89: 3.010 s.
HP49G+: 2.348 s.

'1/(x^4-1)^4'
TI89: 26.127 s.
HP49G+: 4.154 s.

'1/(x^4+1)^4'
TI89: 114.205 s.
HP49G+: 3.414 s. 

The point is, the calculators really use completely different methods
of solving integrals/derivatives.  Both have problems with certain
kinds of problems.  I'd recommend reading through this thread and you
will find lots of interesting things.

http://groups.google.com/group/comp.sys.hp48/browse_thread/thread/4e5d8b811066ba7f/

TW