Any other books or any other book? We usually say any book, and not any books, but when we put other, we seem to say any other books instead of any other book. Are both sentences equivalent or not? Why would one be grammatically incorrect?
Both "any other book" and "any other books" are grammatical. As usual, the singular is speaking about one book, and the plural is speaking about more than one.
Here are two examples:
"Is there any other book on the subject?" is asked by a speaker who may expect an answer of "no", or the name of one book.
"Are there any other books on the subject?" is asked by a speaker who may expect an answer naming several books.