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问题: 函数8

函数8

解答:

(1)
令x=0,y=0
f(0)+f(0)=f(0),f(0)=0
令y=-x,
f(x)+f(-x)=f(0)=0
f(-x)=-f(x)
f(x)是奇函数

(2)
设-1<x1<x2<1,
则x2-x1>0,1+x1>0,1-x2>0
(1+x1)(1-x2)=1+x1-x2-x1x2>0
1-x1x2>x2-x1>0
-1<(x1-x2)/(1-x1x2)<0

f(x1)-f(x2)=f(x1)+f(-x2)=f[(x1-x2)/(1-x1x2)]>0
f(x1)>f(x2)

f(x)单调递减