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

思路解析:由f(sinx)=3-cos2x=3-(1-2sin²x)=2+2sin²x,

∴f(cosx)=2+2cos²x=2+cos2x+1=3+cos2x.

∴选C.

答案:C