设f(sin(x/2))=1+cosx,求f(cosx)
问题描述：
设f(sin(x/2))=1+cosx,求f(cosx)
答
f[sin(x/2)]=1+cos x
=1+1-2[sin(x/2)]^2
=2-2[sin(x/2)]^2
f(cos x)=2-2(cos x)^2