y=2+cos2x/2-cos2x =(4-2+cos2x)/(2-cos2x) =4/(2-cos2x)+(-2+cos2x)/(2-cos2x)=4/(2-cos2x) -1-1≤cos2x≤11≤2-cos2x≤3所以 1/3≤1/(2-cos2x)≤1所以 4/3≤4/(2-cos2x)≤4所以1/3≤4/(2-cos2x)-1≤3即值域为[1/...