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
やすくなかったです
It requires us to answer
やすくありませんでした
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?
やすくありませんでした
is more formal and often used in a written format, so it's preferred to use if you are writing a book, an essay etc. It also completely removes the casual tone, so if you are speaking with someone and want to show that you definitely look up to the person and you are being formal, I would use the formal version (e.g. speaking with CEO of your company, etc). It doesn't really change the strength of denial. – kabichan Jan 24 '20 at 18:03