I recently started learning Chinese and my teachers use English as a second language. I noticed that many of them use the phrase "Let's back to (page XYZ)" as opposed to "Let's go back to (page XYZ)". I had been speaking English for about 20 years so far and never stumbled upon this phrase, but Wiktionary says it's a valid verb:
(intransitive) To go in the reverse direction. quotations ▼
the train backed into the station; the horse refuses to back
So, is "go" needed here?
"Let's" behaves like a modal, and always requires a verb (in the infinitive, or base form.
"Let's back to page 3" is not grammatical in any variety of English that I am aware of.
"Back" can be a verb, but I've only ever heard it in the sense of (physically) moving backwards, not just meaning "go back". It doesn't make sense in that example.
According to the Cambridge Dictionary, back as a verb can mean to (cause to) move backwards. I would only use this word to mean reversing a vehicle.
If I were to talk about moving my own body backwards, I would say go back. Similarly, if I were talking about returning to pages in a book that I have already read, I would say go back.
Back can be a verb, but most of its definitions have nothing to do with "go back". The most similar meaning is to "go back" is to move/make something backwards and the structure is obviously different - it is typically
back (verb) + noun + preposition
rather than
back (verb) + preposition
Therefore, I don't think your teacher used a correct expression.
