Formal language needs to be present in a Rhetorical Precis.
Formal language is the type of language used in professional or educational settings. it is free of slang, conversational phrasing, and personal comments. First person (such as "I" or "we" statements) is not used in formal langauge.
By contrast, informal language is casual and therefore used in conversation. It features contractions, slang, and the use of the first person. It is not appropriate when writing an essay or a piece such as a Rhetorical Precis.