1. Any of the two books is useful.
2. Either of the two books is useful.
3. Either book is useful.
Are the above sentences correct?
Thank you very much.
Merry Xmas to you.
I would not use the word any if there were only two choices.
I would say: "Each of the two books is useful," or your sentences numbers 2 & 3.
Using either implies that you will use one or the other.
Using each implies that you can use one, the other, or both.