Billy Joel expanded his musical palette and dug deep into his own life for his third album. “The Entertainer” boldly addresses his feelings about the music business, using brisk acoustic guitar and a thumping beat to snarl at the suits who shortened “Piano Man” for radio play. He has a ball on “Root Beer Rag,” a frantic ragtime instrumental that sounds like the work of two pianists, while “Los Angelenos” rides a slinky groove, pulsing electric piano, and cool blasts of organ.