How to recover calendar entries and books in iPad 2

[Borong]

Help! I just updated my iPad to iOS 5.1 and lost all my caledar entries and purchased books. How can I recover them?

 

[DaEbLe]

Welcome to iPF!
there are a multitude of ways depending on tons of various situations, but easiest way is to do a restore through itunes.
Otherwise there are variations if you use any sycn options to the cloud.
Have a good time on iPF