已知f(tanx)=cos2x,则f(-根号2除以2)=?

问题描述:

已知f(tanx)=cos2x,则f(-根号2除以2)=?

cos2x=(1-tan&sup2x)/(1+tan&sup2x)
所以f(x)=(1-x&sup2)/(1+x&sup2)
f(-√2/2)=(1-1/2)/(1+1/2)
=1/3