y=√2sin(2x+π／4)-1/2cos²x
=√2[sin(2x)cos(π/4)+cos(2x)sin(π/4)]-1/2cos²x
=√2[sin(2x)·√2/2+cos(2x)·√2/2]-1/2·(cos2x-1)/2
=[sin(2x)+cos(2x)]-1/4·cos2x+1/4
=sin(2x)+3/4·cos(2x)+1/4
=√[1²+(3/4)²]sin(2x+φ) （辅助角公式）
=5/4·sin(2x+φ)