解决y=sin2x-cos2x的导数是?要正确的步骤

---

y=sin2x-cos2x
y'=(sin2x-cos2x)'=(sin2x)'拆物-(cos2x)'
=cos2x*(2x)'+sin2x(2x)'
=2cos2x+2sin2x
=2√旅贺液2(√2/2cos2x+√2/拍纤2sin2x)
=2√2sin(2x+π/4)

---

dy=2cos2x+2sin2x

---

答案是2√2cos(2x-4/π)，步骤是什么

---