已知f(x)是定义在[-1,1]上的奇函数. 当a, b∈[-1,1],且a+b≠0时,

已知f(x)是定义在[-1,1]上的奇函数. 当a, b∈[-1,1],且a+b≠0时,有

(1)判断函数f(x)的的单调性,并给以证明;

(2)若f(1)=1,且f(x)≤m2-2bm+1对所有x∈[-1,1],b∈[-1,1]恒成立,求实数m的取值范围.

答案

(1)见解析(2)(-,-2]∪{0}∪[2,+)


解析:

(1)证明:设x1,x2∈[-1,1],且x1<x2,

∵x1<x2,∴x1-x2<0,又∵f(x)是奇数,∴f(-x2)=-f(x2),

即f(x1)< f(x2).故f(x)在[-1,1]上为增函数.

(2)解:∵f(1)=1且f(x )在[-1,1]上为增函数,所以对x∈[-1,1],有f(x)≤f(1)=1.由题意,对所有的x∈[-1,1],b∈[-1,1],有f(x)≤m2-2bm+1恒成立,

所以m2-2bm+1≥1m2-2bm≥0.

记g(b)=-2mb+m2,对所有的b∈[-1,1],要g(b)≥0恒成立.只需

 m∈(-,-2]∪{0}∪[2,+).

所以实数m的取值范围是:m∈(-,-2]∪{0}∪[2,+).

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