已知函数f(x)满足f(cosX)=cos2x,则 - 知识问答

已知函数f(x)满足f(cosX)=cos2x,则f（sin165°）=

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已知函数f(x)满足f(cosX)=cos2x,则f（sin165°）=
sin165° = cos75°
f(sin165°)
= f(cos75°)
= cos150°
= - cos30°
= - √3/2

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