RMAN was used to clone an Oracle 10g RAC database from a source database SOURCEC3 to a target database TARGETC3 using the DUPLICATE DATABASE feature. The procedure involved preparing the source and target databases, identifying necessary archive log backups, restoring the database to a single-instance target, and then converting it to a RAC database by adding redo logs and enabling cluster functionality. Post-clone tasks verified the successful conversion to a RAC database and started required processes.