HP49 offer options to the user choose between ALGEBRAIC or RPN mode.
To change HP49 Operating Mode:
Press  ( the key [H] )
and it will show a screen like the one in the picture.
So press  and choose the option sown.
Yo can also change mode pressing the key 
( the kew [W] )
Pressing you can also access flags
and other menus, as shown in picture
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