Here is one derivation that works. Here is one derivation that works.
Every atomic sentence is an and-or sentence.
Probably the easiest way to prove this is to exploit the technique used on p. 226- 227 of the text to show a related fact. Say that P has no connectives. This completes the base case. This completes the induction step, and so the claim is proved. We proceed by induction on the number of letters in the sentence.