??????,)421(??t,对称轴为bt?1当21?b时,??tgy?在??????4,21上是增函数,bgy?????????41321min…(7分)2当421??b时,??tgy?在??????b,21上是减函数,在??4,b上是增函数,??2min3bbgy???……………(9分)3当4?b时,??tgy?在??????4,21上是减函数,??bgy8194min???…(11分)综上所述,?????????????????4,819421,321,4132minbbbbbby……………………(12分)高一数学答案第4页共4页22.(本小题12分)解:(1)∵??xf为R上的奇函数,∴??00?f,即021????ab,解得1?b……………………(2分)∴??axfxx?????1212又????11???ff即aa????????11212122,解得2?a……………………(4分)(2)由(1)知??1212122121?????????xxxxf设21,xx是R上的任意两个实数,且21xx?,则????????121222121211212121122121????????????xxxxxxxfxf………(6分)∵21xx?∴2122xx?∴02212??xx又????0121221???xx∴????021??xfxf即????21xfxf?∴??22121?????xxxf在R上是减函数……………(8分)(3)由(2)??xf为R上的减函数和奇函数故不等式????02222????ktfttf可化为??????222222tkfktfttf??????∴kttt????2222即原问题转化为对任意的Rt?有0232???ktt恒成立,…………………(10分)∴0412????k∴31??k∴实数k的取值范围为?????????31,……………(12分)
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