y=cos(2x-π/2)-cos(x-π/4)=cos2(x-π/4)-cos(x-π/4)=2[cos(x-π/4)]^2-cos(x-π/4)-1令cos(x-π/4)=n则原式为2n^2-n-1=2(n-1/4)^2-9/8-1≤n≤1 -5/4≤n-1/4≤3/4 0≤ (n-1/4)^2≤25/16 0 ≤2(n-1/4)^2≤25/8 -9/8...