f(x)=√2/2cos(2x+π/4)+sin(2x)
=cos(π/4)cos(2x+π/4)+sin(2x)
=1/2cos(2x+π/2)+1/2cos(2x)+sin(2x)
=1/2sin(2x)+1/2cos(2x)
=√2/2sin(2x+π/4)
0≤2x+π/4≤2π
-π/8≤x≤7π/8