解:


···················································

2分


································································· 5分

·············································································· 6分

······················································································· 7分
(1)

的最小正周期

···································································· 8分
(2) 由

得

∴

的单调减区间为

··············································· 10分
(3)

∵

∴
∴

∴

即

的值域为

··············································································· 12分