f(x)=(1-cos²x)²+cos²x=1+cos^4x-2cos^2x+cos^x=cos^4x-cos^2x+1=((cos2x+1)/2)^2-cos^2x+1=(cos^2(2x)+1+2cos(2x))/4-(cos2x+1)/2+1=cos^2(2x)/4+3/4;=(cos4x+1)/8+3/4;=cos4x/8+7/8;∵-1≤cos4x≤1...