f(sinx)=3-cos2x,则f(cosx)=A 3-cos2x B 3-sin2xC 3+cos2x D 3+sin2x

来源：学生作业帮助网编辑：作业帮时间：2024/11/16 10:46:49

f(sinx)=3-cos2x,则f(cosx)=A 3-cos2x B 3-sin2xC 3+cos2x D 3+sin2x
f(sinx)=3-cos2x,则f(cosx)=
A 3-cos2x B 3-sin2x
C 3+cos2x D 3+sin2x

f(sinx)=3-cos2x,则f(cosx)=A 3-cos2x B 3-sin2xC 3+cos2x D 3+sin2x
f(cosx)= f(sin(90-x))=3-cos(2(90-x))
=3-cos(180-2x)=3+cos2x
或f(cosx)= f(sin(90+x))=3-cos(2(90+x))
=3-cos(180+2x)=3+cos2x
选C

倍角公式
Cos2A==1-2Sin^2 a= 2Cos^2 a -1
f(sinx)=3-cos2x
f(sinx)=3-(1-2sin^2 x)
即f(x)=3-(1-2x^2)
f(cosx)= 3-（1-2cos^2 x)
f(cosx)= 3+（2cos^2 x-1)
f(cosx)= 3+cos2x
选C

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