Question

若f(sinx)=3-cos2x,则f(cosx)等于(    )

A.3-cos2x               B.3-sin2x             C.3+cos2x             D.3+sin2x

Answer 1

解析:f(sinx)=3-(1-2sin²x)=2+2sin²x,

∴f(x)=2+2x².

∴f(cosx)=2+2cos²x

=2+2·=3+cos2x.

答案:C