Does "Keep positive" in meaning of "be an optimist" works
The context is, when someone was failed in an exam, and I want to encourage him for the second chance that has.
Does "Keep positive" in meaning of "be an optimist" works
The context is, when someone was failed in an exam, and I want to encourage him for the second chance that has.
In my opinion, "Stay positive" is a bit more common and natural-sounding than "Keep positive", although the Ngram indicates that might be a relatively recent trend.
As for what the expression means, you can say that as:
or:
but I would avoid:
(In other words, use an article with the noun; otherwise, use the adjectival form of the word.)