4cos??t1?t2?2?sin???8?∴?t1t2?2sin?????16?16sin2??0??，则
AB?t1?t2?16?16sin?sin?22?46，
∴sin??22，∴???4或??3?4.
，∴x???1,3?.
23.解：(1)∵f?x?(2)∵m∴
??1?x?1??3，∴x?1?2?x?1?m?x?3?0的解集为??2,4?，
x?1?x?3?2m，
而
?2x?2,x?3?x?1?x?3??4,?1?x?3??2?2x,x??1，
∴当m
?3时，解集为?2,4?.