ORA-00849 when trying to use AMM in 11g R2 RAC

Hi

we have a 2 node 11.2.0.3 RAC system with following values on both instances

memory_max_target                    big integer 10240M

memory_target                        big integer 8192M

sga_max_size                         big integer 4096M

sga_target                           big integer 0

pga_aggregate_target                 big integer 0

First question: Assuming above numbers are correct, are we using AMM or ASMM? What would be the impact of having PGA_AGGREGATE_TARGET = 0 in this situation?

sqlplus /nolog

connect / as sysdba

show sga

Total System Global Area 4275933184 bytes

Fixed Size                  2233248 bytes

Variable Size             905972832 bytes

Database Buffers         3355443200 bytes

Redo Buffers               12283904 bytes

SQL>

On node-1 we want the instance to use AMM and not ASMM so we set the following