已知f(sinx)=cos2x,则f(1/2)=___,f(cosx)=___

解法一:f(sinx)=cos2x=1-2(sinx)^2
所以f(x)=1-2x^2
f(1/2)=1/2
f(cosx)=1-2(cosx)^2=-cos2x
解法二:f(1/2)=f(sin30')=cos60'=1/2
f(cosx)=f(sin(x+90'))=cos(2x+180')=-cos2x