We can mark the particular books as S1 & S2.
And the other books as B1, B2, B3, B4, B5, B6, B7, B8.
The particular books are always together.
So, we can arrange this (8 + 1) = 9 books in 9! way in the shelf AND the particular books can itself arranged in 2! ways.
So, Total ways = 9! * 2!