已知f(x)是奇函数,f(x+2)=f(x),且当0

来源:学生作业帮助网 编辑:作业帮 时间:2024/05/01 20:09:14

已知f(x)是奇函数,f(x+2)=f(x),且当0
已知f(x)是奇函数,f(x+2)=f(x),且当0

已知f(x)是奇函数,f(x+2)=f(x),且当0
f(x)是奇函数则f(x)=-f(-x)
又f(x+2)=f(x)
a=f(6/5)=f(-4/5+2)=f(-4/5)=-f(4/5)=-lg(4/5)
b=f(3/2)=f(-1/2+2)=f(-1/2)=-f(1/2)=-lg(1/2)
c=f(5/2)=f(2+1/2)=f(1/2)=lg(1/2)
-lg(1/2)>-lg(4/5)>lg(1/2)
所以b>a>c

f(-x)=-f(x)=-f(x+2)
=> f(6/5)=f(1.2)=f(-0.8+2)=f(-0.8)=-f(0.8)=-log0.8=a =log(0.8)^-1=log(5/4)=log1.25
f(3/2)=f(1.5)=f(-0.5+2)=f(-0.5)=-f(0.5)=-log0.5=b=log(0.5)^-1=log2
f(5/2)=f(2.5)=f(2+0.5)=f(0.5)=log 0.5=c

log增函数 2>1.25>0.5 => log2>log1.25>log0.5 =>b>a>0