Why first_lsn of full backup and 1st transaction log backup are same?

Question

shouldn't first_lsn of the 1st transaction log backup be 36000000022400001 instead of 36000000022100001? In this case it equals to first_lsn of full backup.

Answer 1

Why first_lsn of full backup and 1st transaction log backup are same?

Because Full backups never break the log chain. The log backups contain a contiguous sequence of log records regardless of how many Full backups were taken.

The log records in the Full are only there to enable the database to be restored and recovered to the point-in-time at which the backup completed.