函数y=cos^2wx-sin^2wx=COS2WX;周期为π；可知w=1.
f(x)=2sin(wx+π/4)=2sin(x+π/4)；sinx单增区间为[-π/2,π/2],故知,
f（x）单增区间为[-π/4,3π/4],加上2kπ即为单增区间