I am doing the exercises for a course in Japanese, which I cannot attend, because it overlaps with my mandatory course. The exercise requires to form the past negative masu form of i-adjectives. Instead of
It requires us to answer
When to use this form? I suspect it is just an even more polite version, but I searched a lot and cannot find any example of usage for this, so I am somewhat insecure!
Edit: When I learned Japanese in the past (from books) the verb-masu form was always introduced together with the adjective-desu/adjective-kunai desu form. So, as regards to this new adjective-ku-arimasen, when should I prefer it? And should I pair it with verb-masu or with something more polite?