已知f(cosx)=cos1998x,求f(sinx)的值

问题描述:

已知f(cosx)=cos1998x,求f(sinx)的值

f(sinx)=f[cos(π/2-x)]
=cos1998(π/2-x)
=cos(999π-1998x)
=-cos1998x

sinx=cos(π/2-x)
所以,f(sinx)=f[cos(π/2-x)]
=cos1998(π/2-x)
=cos(999π-1998x)
=-cos1998x