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问题: 偶函数

定义在R上的偶函数f(x)满足f(x)满足f(x)=f(x+2),当x∈[3,5]时,f(x)=2-|x-4| , 则( )

解答:

A.
f(sinπ/6)=f(0.5)=f(2+0.5)=f(2+2.5)=1.5
f(cosπ/6)=f(√3/2)=f[2+(√3/2)]=f[4+(√3/2)]=2-(√3/2)<2-(1/2)=1.5
===>f(sinπ/6)>f(cosπ/6)

B.
同理,f(sin1)=f(4+sin1)=2-sin1, f(cos1)=f(4+cos1)=2-cos1
因cos1<sin1,所以f(sin1)<f(cos1)

C.
f(cos2π/3)=f(-0.5)=f(4-0.5)=f(3.5)=1.5
f(sin2π/3)=f(√3/2)<1.5
f(cos2π/3)>(sin2π/3)

D.对
f(sin2)=f(4+sin2)=2-︱sin2︱, f(cos2)=f(4+cos2)=2-︱cos2︱
因︱sin2︱>︱cos2︱
f(cos2)>f(sin2)