the structures you mentioned are usually used when you want to say something like "should" or "be supposed to"
1) What am I to tell my father when he finds out? (what should I tell him?)
2) He is more to be pitied than feared.
It is to be done or; (it should be done or is supposed to be done)
It is to be determined; (it should be determined)
It has to be achieved and so on
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