y=1/2(2sin2xcos2x)=1/2sin4x,T=2π/w=2π/4=π/2,由此可画出图形,最大值为1/2,递增区间为2kπ-π/2<=4x<=2kπ+π/2,化简得kπ/2-π/8<=x<=kπ/2+π/8