tmsh command to configure pool and node in one line ?

Here, Use the ; to separate your commands.

create ltm node 10.10.10.50 ; create ltm pool Sajan-8000 members add { 10.10.10.50:80 } monitor tcp

ltm pool Sajan-8900 {
members {
    10.10.10.50:80 {
        address 10.10.10.50
        session monitor-enabled
        state down
    }
}
monitor tcp
}

Just in case you want to create 2 commands. But you can just go and create it with the pool itself. The node will auto-created.