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