In dragon age origin how do you defeat the brood mother

First make a two people stand at the back rocks, (your mages or rogues.) Make two stand at the front rock, (warriors and rogues.) Keep attacking the mother, (she'll only spit) with far attacks from mages and rogues and warriors at the front. When she screams send the people back on the rocks. This will prevent the tentacles from getting to you. First kill the darkspawn, (still on the rocks) and then the tentacles. Do that each time, which she does it 3 times. +If you have only a little, do not waste the poultices and lyrium as there is a harder fight later on. When I was playing I had 5 five poultices and 3 lyrium. I used them up in that fight but in the harder fight i had 2 poutices and no lyrium!