Chose to be positive (7)
I believe the answer is:
decided
I believe this is a double definition.
'chose' is the first definition.
'positive' is the second definition.
(thesaurus)
'to be' is the link.
(Other definitions for decided that I've seen before include "Definite; agreed" , "Came to a resolution" , "Marked" , "Resolute; settled" , "Determined - settled" .)