f(x)=[2cos^2(x)-1]/2=(1/2)cos(2wx+2φ)
周期为π,w=1,
f(x)=(1/2)cos(2x+2φ)
1/4=(1/2)ccos(π/4+2φ)
os(π/4+2φ)=1/2
π/4+2φ=π/3
φ=π/24
2
f(x)=1/2cos(2x+π/24)
-13π/24+kπ≤x≤-π/48+kπ
单调增区间为：
【 -13π/24+kπ,-π/48+kπ 】