use bignum accuracy => 300;

##</code><code>##

perl -Mbignum=a,50 -le 'print sqrt(20)'
 
##</code><code>##

use bignum accuracy => 50;

print sqrt(20);

##</code><code>##

CentOS release 5.6 (Final)
cat /proc/version
Linux version 2.6.18-238.19.1.el5 (mockbuild@builder10.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-50)) #1 SMP Fri Jul 15 07:31:24 EDT 2011